If you'd like to plot the orbits of solar system bodies, including comets and asteroids, try "Solar System Live" by John Walker, http://www.fourmilab.to/solar/solar.html

You can use "Solar System Live" to plot comets and asteroids as well. Orbital elements of comets can be found at the IAU: Minor Planet Center "Minor Planet & Comet Ephemeris Service" page http://cfa-www.harvard.edu/iau/MPEph/MPEph.html. For instance, you can find the orbital elements for comet Halley by entering 1P/Halley. Select "MPC 8-line" as the "Format for elements output", and cut and paste the orbital elements directly into the Solar System Live site to see where the comet is now. Thus it's easy to see that, although it's only 23 years after its last perihelion, and there are 52 years until the next one, Halley is already at Neptune's orbit, nearly at aphelion: this is an excellent illustration of Kepler's second law. To get side on views, change the Heliocentric latitude to 0 degrees and the longitude to 90 degrees.

Alan Taylor has put together a beautiful image of "All (known) Bodies in the Solar System Larger than 200 Miles in Diameter" (now including a new metric version with everything larger than 320 km in diameter) at http://www.kokogiak.com/gedankengang/2007/03/all-known-bodies-in-solar-system.html. Because this was made in 2007, some of the dwarf planets, like Haumea and Makemake, still have their provisional desgnations.

There's a list of binary asteroids at "Asteroids with Satellites" by Wm. Robert Johnston, http://www.johnstonsarchive.net/astro/asteroidmoons.html

The Earth Impact Database http://www.unb.ca/passc/ImpactDatabase/ lists every confirmed impact crater known

If you need to report a meteor fireball, there's an on-line report form at the International Meteor Organisation's page, http://www.imo.net/fireball/index.html

The Impact Calculator at http://simulator.down2earth.eu/index.html allows you to simulate smashing an asteroid into Earth and see how big a crater your asteroid made. You even get to choose which city you crash into (though unfortunately (!) Sydney is not on the list)

NASA has an information site on Earth impact hazards at "Asteroid and Comet Impact Hazards", http://impact.arc.nasa.gov/; see also the "Near Earth Object Program: Current Risks" http://neo.jpl.nasa.gov/risk/

There is a list of all minor planets and asteroids predicted to approach within 0.2 AU of the Earth during the next 33 years at the IAU Minor Planet Center, "Forthcoming Close Approaches To The Earth", http://cfa-www.harvard.edu/iau/lists/CloseApp.html

The BBC has a news story about 2008 TC3, the asteroid that hit Sudan, at http://news.bbc.co.uk/2/hi/science/nature/7964891.stm

There's an article on "The saga of Asteroid 2004 MN4" at http://impact.arc.nasa.gov/news_detail.cfm?ID=154.

The Association of Space Explorers (ASE), the international organization of astronauts and cosmonauts, is leading the effort to develop a UN treaty and other international mechanisms about asteroid deflection. Their report is available on-line at http://www.space-explorers.org/ATACGR.pdf; it contains a good discussion of the issues involved. Sources for images used:

Background image: Eros, taken by NEAR-Shoemaker, from Astronomy Picture of the Day 2001 February 11 http://antwrp.gsfc.nasa.gov/apod/ap010211.html

Asteroid cover picture: Galileo image of asteroid 951 Gaspra, from APOD 2002 October 27 http://antwrp.gsfc.nasa.gov/apod/ap021027.html

Asteroid orbits: from "Explorations: An Introduction to Astronomy!" by Thomas T. Arny, Fig. 10.4 http://www.mhhe.com/physsci/astronomy/arny/instructor/graphics/ch10/1004.html

NEAR trajectory: from NEAR Mission Profile at the NASA Planetary Missions site http://nssdc.gsfc.nasa.gov/planetary/mission/near/near_traj.html

Eros animations: from NEAR Eros Animations http://nssdc.gsfc.nasa.gov/planetary/mission/near/near_eros_anim.html

Kirkwood gaps: from "Explorations: An Introduction to Astronomy!" by Thomas T. Arny, Fig. 10.7 http://www.mhhe.com/physsci/astronomy/arny/instructor/graphics/ch10/1007.html

Differentiation: from "Explorations: An Introduction to Astronomy!" by Thomas T. Arny, Fig. 10.6 http://www.mhhe.com/physsci/astronomy/arny/instructor/graphics/ch10/1006.html

Asteroid shapes: Mathilde, Gaspra, and Ida, from Astronomy Picture of the Day March 13, 1998 http://antwrp.gsfc.nasa.gov/apod/ap980313.html

Mathilde flyby: NEAR images: animation and video http://near.jhuapl.edu/Images/.Anim.html

Animation and model of Vesta: from the Hubble News Center Archive http://hubblesite.org/newscenter/archive/1997/27/

Binary asteroid: Astronomy Picture of the Day 2004 June 19 http://antwrp.gsfc.nasa.gov/apod/ap040619.html

Tidal disruption simulation: from Walsh & Richardson 2006, "Binary near-Earth asteroid formation: Rubble pile model of tidal disruptions", Icarus 180, 201

Patroclus and Menoetius: Frank Marchis "Study of Patroclus and Menoetius: A Double Trojan System" http://astro.berkeley.edu/~fmarchis/Science/Asteroids/Patroclus/

Asbolus: Hubble Site release STScI-2000-31 http://hubblesite.org/newscenter/archive/releases/solar-system/kuiper-belt-object/2000/31/

Comet cover image: Comet West from Astronomy Picture of the Day 26 August 1995 http://antwrp.gsfc.nasa.gov/apod/ap950826.html

Orbit of comet LINEAR: from Chandra X-ray Observatory Photo Album http://chandra.harvard.edu/photo/cycle1/c1999s4/more.html

Orbit of Comet Halley: from "Comet Halley" http://csep10.phys.utk.edu/astr161/lect/comets/halley.html

Coma: Hale-Bopp, from Astronomy Picture of the Day February 12, 1997 http://antwrp.gsfc.nasa.gov/apod/ap970212.html

Comet's tail: Hale-Bopp, from Astronomy Picture of the Day 27 December 2000 http://antwrp.gsfc.nasa.gov/apod/ap001227.html

Two tails: from http://www.physics.fsu.edu/courses/spring99/ast1002h/solarsystem/fig16-14/fig16-142.htm. Hale-Bopp in 1997: Jerry Lodriguss, from Astronomy Picture of the Day 2007 March 31 http://antwrp.gsfc.nasa.gov/apod/ap070331.html

Comet McNaught: picture by Robert McNaught, from Astronomy Picture of the Day 2007 January 22 http://antwrp.gsfc.nasa.gov/apod/ap070122.html; comet over Bendalong, photo by Alain Picard

McNaught's tail: Astronomy Picture of the Day 2007 February 1 http://antwrp.gsfc.nasa.gov/apod/ap070201.html

Deep Impact image: from Deep Impact gallery http://deepimpact.jpl.nasa.gov/gallery/index.cfm

SOHO comet: from SOHO gallery http://sohowww.nascom.nasa.gov/gallery/images/xmascomet.html

Oort cloud/Kuiper Belt title image: artist's conception of the Kuiper Belt object Quaoar, from Hubble Site News Center Archive, http://hubblesite.org/newscenter/archive/2002/17/

Kuiper belt: from Views of the Solar System by Calvin Hamilton http://www.solarviews.com/cap/index/oortcloud1.html

Oort cloud/Kuiper belt: from "Explorations: An Introduction to Astronomy!" by Thomas T. Arny, Fig. 7.4 http://www.mhhe.com/physsci/astronomy/arny/instructor/graphics/ch07/0704.html

Trans-Neptunian objects: Wikipedia http://en.wikipedia.org/wiki/Trans-Neptunian_Objects

Orbits of TNOs: Wikipedia http://en.wikipedia.org/wiki/Scattered_disk

A list of known trans-Neptunian objects can be found at http://www.johnstonsarchive.net/astro/tnos.html

Meteor title image: Leonids over Uluru, from Astronomy Picture of the Day 30 October 2002 http://antwrp.gsfc.nasa.gov/apod/ap021030.html

Fireball: Leonid fireball, from Astronomy Picture of the Day 2 December 1999 http://antwrp.gsfc.nasa.gov/apod/ap991202.html

The Great Daylight Fireball: from APOD 2009 Mar 2 http://antwrp.gsfc.nasa.gov/apod/ap090302.html

Meteoroid endpoints: re-drawn from "Meteorites: A journey through space and time" by Bevan and de Laeter, p. 31

Crater formation: from The Terrestrial Planets by Gareth Wynn-Williams http://www.ifa.hawaii.edu/~wynnwill/110/images/crater_formation.gif

Meteorite images: from "Exploring Meteorite Mysteries" http://www-curator.jsc.nasa.gov/outreach1/expmetmys/slideset/Slides35-42.htm

Dust grain: from "Stardust: Catching particles in Space", http://stardust.jpl.nasa.gov/science/sd-particle.html

Isochron: from "The Talk.Origins Archive: The Age of the Earth" by Chris Stassen http://www.talkorigins.org/faqs/faq-age-of-earth.html

Images of 2008 TC3, from Nature vol 458, pp 401 and 485

Impacts and life: Table 1 from "How common are habitable planets" by Jack Lissauer, 1999, Nature 402, C11, available at http://www.kepler.arc.nasa.gov/papers.html

Animation of K-T impact: from The Wright Center for Science Education, Tufts University, "It's Judgement Day" http://www.tufts.edu/as/wright_center/impact/impacta.html

Illustrations of K-T impact: from "The Impact that Wiped Out the Dinosaur" by William Hartmann http://www.psi.edu/projects/ktimpact/ktimpact.html

Comet Shoemaker-Levy: Hubble images, from HubbleSite News Archive, http://hubblesite.org/newscenter/newsdesk/archive/releases/1994/26/ and http://hubblesite.org/newscenter/newsdesk/archive/releases/1994/32/

Crater chains: Ganymede: from Astronomy Picture of the Day, 2001 December 15, http://antwrp.gsfc.nasa.gov/apod/ap011215.html. Moon: from Lunar Photo of the Day, January 27 2004, http://www.lpod.org/archive/2004/01/LPOD-2004-01-27.htm

Torino Impact Scale: from "Asteroid and Comet Impact Hazards", http://impact.arc.nasa.gov/torino.cfm

2004 MN4 orbit predictions: from "Radar observations refine the future motion of Asteroid 2004 MN4", http://neo.jpl.nasa.gov/news/news149.html

Positions of 2004 MN4 and the planets: from Solar System Live http://www.fourmilab.to/cgi-bin/uncgi/Solar