In my opinion there's no question, Armaholic is THE
place. Its simply put the best gaming community I've ever seen. The amount of skilled people exchanging information and mods here and on the BI forum is astonishing.
On the bits and pieces thing, I agree with W0lle, but one site thats helped me alot too, is the BI community WIKI
Apart from that the OFPEC site and forum
is also nice, and as mentioned above the BI forum
is also a great source, obviously :)