Canco :
Benevolence :
The Ti (Boost) is a faster clock speed which will improve graphics performance.
For RAM, any DDR3 @ 1600 should work with your CPU/motherboard, but no faster unless you want to enter the wonderful world of overclocking.
Given that you only have 2 slots, an 8GB (2x4) or 16GB (2x8) should work nicely. The more RAM you have, the better. I would look for a DDR3 1600MHz with low timings.
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&Description=ddr3+1600&N=-1&isNodeId=1
Would the intel core i5 2500K work aswell?
Yes, your MB is a LGA 1155 and will work with 2nd and 3rd gen CPUs, so a i5 2500k would work fine.
Get whatever video card you want to get, any 650 would do you OK. The Boost version is a better buy because you get more for your money, a better bang for your bucks if you know what I mean. The 650 Boost has the 660 core in it (GK 106), much better than the 650 (GK 107) core in the other 2, and not that much more cost compared to the performance gain. It is basically a de-tuned 660.
You could likely get by with a HD 7770 if you really want to save money. Perhaps start a new thread like "Minimum graphics card needed to play WOW on ultra settings", you may get more info and find just what you are looking for.