ChartFox Free access to charts for many countries. Requires login with VATSIM account. Update
SkyVector.com Sectionals/VFR charts/IFR enroute charts high and low/TAC/WAC. Has a great flight planner. For USA also links to airport charts. Very useful site. Update
AIRnav AIRnav.com is a great site with every chart you can imagine including fine details about any US airport! USA Only. Update
AVSIM Do an extended search in the File Library and type in Matt Fox as the desired author, and "sectional" as the description. This will bring up a multitude of Hi res sectionals and Terminal Area Charts. A MUST HAVE for VFR Flyers! Update
DAFIF site National Geospatial-Intelligence Agency DAFIF Flight data site. Info and services for national, military and civil aircrews. A mine of information! Update
European AIS Database This is the European AIS Database website. Lots of charts, but you'll need to register (free) Update
simBrief Dispatching system giving you a complete flight plans - featuring detailed fuel planning, weather forecasts, current NOTAMs, ETOPS calculations, and much more. Update
FlightAware.com This is an amazing site. Submit dep/arr airports and this site returns the last actual real world routings. US based but will provide international flights to and from the US also. Update
CheckWX Weather info at airports - with METAR, TAF, trends and historical graphs, timezone (incl sunrise/sunset for finding the golden hour!) Update
Fltplan.com Fltplan.com is an excellent resource actually used for real world flight planning, however is available for us simmers as well. You have to register (don't worry it's free) but it's well worth it! This is the best site to find USA Government Preferred routing. Update
FS Build.com Another highly recommended payware flight planning utility Update
GoodWay Flight Planner Freeware flight planner software for X-Plane, FMS exporter for X-Plane. Shareware version also available with extra features. Update
Route Finder Route Finder is a simple user interface to generate flight plans around the world (not entered and verified by any human as I understand it) Update
vroute.info Great online flying tool for flight planning etc. Update
Other Flight Planning
Eurocontrol's Central Flow Management Unit Real world flight plan verification. Use the links in the Flight Planning section to enter a flight plan with/to/from Europe and to see if it would be accepted in the real world. Update
openNav Database of mainly lat/lon of airports and navaids (incl waypoints) - and some charts as well Update