I'm pretty sure we used to have a list for race specific forums, but I couldn't find it (searchfu is not strong with this one...)
anyway here's the forums that I have previously used and absued. If anyone has any others add them in and I'll update the list. Maybe someone important can sticky the list.
MARINES (LOYALLIST AND RENEGADE)
DAEMONS (technically WHFB daemons, but has some good 40K stuff)
the daemonic legion
ELDAR AND DARK ELDAR