I recently dinged 80 and am now concentrating on geming my gear. I have looked throught the posts and have found a lot of useful information. My questions is this...Is there a site, post or location to compare all the gems available? There are a lot of places to get gems, but I can't find a place that listed them all.
The main loot list has a good gem list. It's not fully comprehensive, but it gives you a good idea.
On the other hand, don't just gem the gem. Look at your socket bonuses too. It's great if it's a blue socket - stick a stam gem in there and forget about it - but what about the red and yellow ones? Sometimes you won't care about the crummy socket bonus, and you'll stam it up. Sometimes you'll say "gee, the socket bonus is stam anyway", and go with a purple or a green that gives you stam and something else; some of those socket bonuses will make up most of the stam difference, so you might as well turn the 4-6 missing stam into 8 dodge rating or something along those lines, huh?
Your gem slots are also your bumper against dropping below 540 defense. If you take a defense hit, consider swapping stam for def gems instead of having to downgrade other gear.
If your lacking 540 def, then gem accordingly to raise it to that mark. if you are at a comfortable def rating then fill any blue sockets with stam gems, gemming avoidance isnt worth it after diminishing. If your socket bonus is worth grabbing, for red the best bet is the 8 exp and 12 stam gems, for yellow, maybe hit or def stam. In the end its your choice