Elitist Jerks is a guild on Mal’Ganis US. Why do you need to know about their website? Because its got the best theorycrafting going.
You can find Elitist Jerks at http://elitistjerks.com/.
Click on Forums and scroll down to Class Mechanics and choose your class. In the forum for your class you will find a number of threads that will include a number of guides for your class and spec. I strongly recommend reading them and taking on their advice.
These guides are some of the best advice you can find on the web. They are normally correct and corrected in that people keep them up to date. The theorycrafting behind them is sound and they are accessible. That’s not to say they are 100% accurate. You can exercise judgement – but generally they are right so if you disagree you want to think carefully about why. For example I don’t have the EJ Holy build on my priest, but that’s based on years of playing her and knowing how I play. I don’t take Inner Focus even though it’s a good spell because I’ve never managed to work it into my play effectively. I know it’s a lack on my part, but I feel I would be better increasing the throughput of the spells I do use.
Elitist Jerks guides normally cover talents, stats, gems and enchants and sometimes gear (even if its just trinkets). For example the Retribution paladin guide will explain possible builds, what stats are good and which ones are just ‘meh’ and what caps you need for hit and expertise.
We had an application from a Warlock with Egg of Mortal Essence. My first thought – ‘why do you have a healing trinket?’. It turns out that the Egg is not bad for warlocks pre-raid because of all that lovely spellpower. Its on a list from EJ. This I would accept as a good reason to have the Egg. I don’t have time to research every class and spec, so I would take ‘because its on this thread from EJ as a good reason that you can see here http://elitistjerks.com/f80/t37900-dots_you_affliction_warlock_thread/#Trinkets
A note of caution. What I also noticed is that Sundial of the Exile was on the list too, and higher up. The lock had chosen the Egg over that even though it cost the same number of badges! Needless to say we didn’t trial the warlock because clearly he hadn’t looked properly at his gear. Read the advice carefully and in full!