I'd suggest Gateworld; between it and the Stargate Solutions wiki, just about any Stargate question I've ever had has been easily answered.

Here's the Gateworld index for Atlantis: http://www.gateworld.net/atlantis/

And the Wiki, if you're curious, though their focus is obviously centered on SG-1 and the Atlantis stuff is mostly referenced in terms of how it affects the parent show: http://www.stargate-sg1-solutions.com/wiki/Main_Page