No need to go for an i7 build for gaming. $1800 is more than you will need for a good rig.
CPU:i5 760 ($210)
Motherboard: Asus P7P55D E Pro ($180)
PSU: Corsair 750W ($100)
Case: Antec 300/HAF 922/CM 690 ($60 - $90)
HDD: Samsung Spinpoint F3 500gb/1TB ($55/$75)
RAM: 4gb 1600mhz G Skill Eco RAM CL7 ($105)
DVD Drive: Any will do, about $25
GPU: GTX460/GTX 470/ATI 5850/ATI 5870 ($230 - $390)
Total: $900 - $1000
The cases listed are good quality cases, I would go with the HAF 922 as you can afford it and it is a nice size with great airflow.
When it comes to GPU, you have options depending on what resolution you play at.
I have assumed you are playing at 1920 x 1080, all the cards listed will cope, the GTX 460 being the weakest of the bunch, but when SLI'd it is excellent (though I believe WoW does not make use of 2 card set ups...however, a GTX 460 on its own is more than capable of handling that game).
If it were me, I would be looking at either the GTX 460, GTX 470 or the ATI 5870. Due to having a motherboard that allows 2 card set up when required in the future, I think the once very nice card 5850 is no longer a great buy - it is a bit more powerful than the GTX 460, but when two cards go together the GTX 460s are superior and cheaper.
This sort of build will cope with anything around, more than you need for the games you listed,but plenty of spare power for anything that may come out.