With all this patch 3.1 PTR news and speculation flying around, it's useful to have a place that simply accumulates hard information on spells, items, talents, quests, and so on. Wowhead's new PTR site is that place. This is the first time to my knowledge that they've done a PTR-specific site; there was a site for the WotLK beta as well, which was very handy.
On the PTR site you can find a page for basically everything as it is in the latest PTR build. I find the talent calculator especially useful. There is also a nicely formatted page listing everything new in patch 3.1, which some people may find helpful in building their Ulduar wish lists. My Ulduar wish list is something like "Please, oh great RNG, give me something without a ton of Armor Penetration on it for my Unholy DK" (actually, I'll probably just give in and respec Blood+MoG).
We've been using the PTR site since it went up to provide tooltips for new and updated spells and items. If you need some 3.1 information, take a look.
Patch 3.1 brings us Ulduar, dual specs, significant changes to all the classes, and more! We've got you covered from top to bottom with our Guide to Patch 3.1.