General

Bobs Track Builder - Forums hosted at Race Sim Central.

First Community Support Site - A great site maintained by AolBites.

rFactor

To help in the process of finishing off your tracks, here are a few handy links.

F.A.Q - Wiki on all terms used and some great info in here.

Setting AIW - how to set paths for AI cars.
AIW and CAM editor - Set AIW and Cameras using this utility.

Vis Groups - fine tune your FPS using vis groups to control how objects appear in your scene.

Richard Burns Rally

Blackhole Motorsports - Richard Burns Track Building forums.