Combat Flight Simulator lets you import scenery and planes constructed for Microsoft's Flight Simulator 98 (and older). There is a vast array of free scenery on the Internet - most places on Earth have been recreated by enthusiasts armed with scenery creation software packages, maps, scanned images and satellite photos.
Comox Valley Flight Simulator Stopover
The Real Florida Scenery Group
Forkboy2's zplanes (multi-player planes!)
Sim Combat (includes planes and stuff especially for CFS)
The Independant FS98 Site - Flight Simulation Information And Files (includes stuff especially for CFS)
email me any relevant links