Avweb:
http://www.avweb.com/
and their list of aviation websites:
http://www.avweb.com/toc/netsites.html
and, of course, that aviation mega-site, "Landings":
http://www.landings.com/

Aviation Week:
http://www.aviationnow.com/

AOPA:
http://www.aopa.org/

EAA:
http://www.eaa.org/
fuel prices and flight planning:
http://www.airnav.com/plan/fuel-stops.html

flight.com:
http://www.flight.com/

DUATS:
http://www.duats.com/duats.cgi

NOAA weather:
http://weather.noaa.gov/
NOAA METAR weather:
http://weather.noaa.gov/weather/coded.html
Current weather at FTW (fill in your airport identifier):
http://weather.noaa.gov/weather/current/KWVI.html

Aviation weather:
http://adds.awc-kc.noaa.gov/

Weather channel:
http://www.weather.com/activities/aviation/

"pilot weather briefing":
http://members.aol.com/rlattery/pilot.htm

"PilotWeather":
http://www.pilotweather.com/avibinf/index?wxcity=US%3B96141&partner=partner&
metrix=metrix

weather satellite images (world view-cool!):
http://www.intellicast.com/LocalWeather/World/UnitedStates/World/

Canadian aviation weather:
http://www.cmc.ec.gc.ca/cmc/redirect_cmc.html

Track a flight:
http://www.airspacemag.com/ASM/Web/Utils/webtrax.html
and see an example:
http://216.33.28.152/cgi-bin/client2.cgi

here's another flight tracker:
http://www.trip.com/trs/trip/flighttracker/flight_tracker_home.xsl

and another:
http://airtravelcenter.com/query2.htm

flight planner:
http://www.aerochart.com/mapping/route/index.cfm
see approach plates (NOS) from this same website:
http://aeroplanner.com/flightplanning/approachplates.cfm

airport directory:
http://www.airstripamerica.com/

FAA ATC system command center (slow, of course-it's the government):
http://www.fly.faa.gov/flyFAA/index.html
FAA:
http://www.faa.gov/
FAA aviation registry:
http://registry.faa.gov./frame.htm
FAA incident data:
http://nasdac.faa.gov/asp/asy_fids.asp

NTSB:
http://www.ntsb.gov/
NTSB accident database:
http://www.ntsb.gov/NTSB/query.asp
aviation safety site:
http://aviation-safety.net/index.shtml

ERAU aviation website reference page:
http://www.erau.edu/libraries/virtual/Aviation/

"Aviation's best sites":
http://www.aircraftbuyer.com/sites.html

another "best aviation sites" list:
http://www.bestaviationsites.com/bas/index.html

and its number one site:
http://www.crewstart.com/

aviation "yellow pages":
http://www.aviationfinder.com/

O'HareTracon:
http://www.thetracon.com/

$100 hamburger (airport restaurants, etc.):
http://www.100dollarhamburger.com/

ASO, aircraft for sale:
http://www.aso.com/