Motorsportgaming.com - Contains cars and patches for download. - http://www.motorsportgaming.com/main/games/grandprix4/
AlphaF1 - Grand Prix 4 - Comprehensive presentation of the game includes the latest news and screen shots. Also with a forum and a chat. - http://koti.mbnet.fi/racing/gp4/index2.shtml
RaceSimulations - Offers downloads including cars, setups, tracks, and editors. - http://www.racesimulations.com/index.php?game=GP4
grandprixgames.org - Contains cars, tracks, setups, and utilities for download plus game information and forums. - http://www.grandprixgames.org
Official Grand Prix 4 site - Includes screen shots, movies and game information. - http://www.grandprixgames.com