I have been able to play Diablo 3 on low settings with 25-30fps (tolerable) on a laptop with an i3-2350, 4GB of RAM and an Intel HD 3000 integrated graphics controller. Does it look good? No, but it allowed me to play at work.
Edit: if you're not an AMD CPU fan, you can get this laptop with an i5-2450m and AMD 7670m graphics card as well for $495 after rebate. It is refurbished but I've bought refurbs from TigerDirect before with no issues: http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2383674&CatId=17