If you are playing at 1920x1080 or below the HD 6770 will probably keep your frame rates above 60. So if you can't spend more than 100 gold, go back to the previous page and click on one of those HD 6770 Newegg links.
If you got more than 100 gold (but less than 200), then the HD 6870 is the right weapon for the job. It should do the job at reolutions up to and including 1920x1200. These rebates all expire on the day Diablo III comes out so make sure to get yours now!
XFX HD 6870 1GB w/Dirt3 for $149.99 after $30 MIR card (exp. 5/15) & FREE shipping
Sapphire HD 6870 1GB w/Dirt3 for $149.99 after $10 MIR card (exp. 5/15) & FREE shipping
XFX Double Dissipation HD 6870 1GB w/Dirt3 for $159.99 after $30 MIR card (exp. 5/15) & FREE shipping
If you feel like you need a little more power than HD 6870, then I recommend a fine GTX 480 or HD 7850. The GTX 480 is more powerful and cheaper than the HD 7850, but the GTX 480 is pretty rare. Newegg only has the one below in stock.
If you are rocking a 30" monitor with a 2560x1600 resolution monitor but you have less than 300 gold to spend, you will need the GTX 570 so you can run Diablo III with max settings and anti-aliasing. Take note of the cheapest one because it is Evga's Superclocked model; which means that it is faster right out of the box than the regular GTX 570s.
Evga Superclocked GTX 570 1,280MB for $279.99 after $20 MIR card (exp. 5/15) & FREE shipping
Evga GTX 570 1,280MB for $282.55 after $25 MIR card (exp. 5/15) & $7.56 shipping
ECS GTX 570 1,280MB for $287.55 after $10 MIR check (exp. 5/21) & $7.56 shipping
For truly epic heroes with more than 300 gold (and a huge 2560x1600 monitor) the HD 7870 is the next step up the ladder... to madness! The IceQ X model has a better cooling design than the other HIS.
Rich wizards and monks that have pledged their allegiance to Nvidia the green goddess, can procure the brand new GTX 670. How new? It was announced, released and put on sale yesterday. This card should be able to handle your epic main monitor and an additional monitor for chatting or other simple tasks.
Now that I have revealed the mysterious truths of Diablo III video cards to you, it is time for me to prepare for the epic adventure that lies anon. Look for me on your server if you wish. My battletag is mentok1982#1212 and I will playing a female wizard by the name of Elvira Sorrow.