The most important site ever is right here, STING. Not only am I a member, I'm also part of the Tech Team. If there were a decent 'cocker owner's group, I'd link you to them...
Speaking of cockers, if it weren't for G3PB.com, I wouldn't even have mine... thanks again, Terry =^) I can't say enough good things about them.
Doc's Machine is pretty cool, too, I really think Doc's my hero. Rec and Stock Class aficionados can appreciate Durtydan.com.  If you want more paintball info than you can shake a couple of sticks at, check out WARPIG and Ravi's page.

And, for the sake of promoting their items, here are a few manufacturer's links...
Brass Eagle, yeah, they come first, since they helped get me into paintball in the first place.
JT USA and Worr Games Products... you know who these guys are!
Component Concepts, Inc. you *might* not know, since the world seems hell bent on embracing electros and higher ROF, pumps got lost in the shuffle...