This list is only small at the moment, but is likely to become a lot longer in the near future. If you have any suggestions feel free to contact me.

http://gtainside.com
http://gta3.gamigo.de
www.gtagarage.com
www.gta-downloads.com
www.gtatools.com
http://mtavc.com
www.altech.com.au
www.cjb.net