Frankly, I think an Intel build is perfect for your purposes. Diablo 3 only uses 2 cores, like most Blizzard games, and desktop work doesn't take much. What you really want to do is fit an SSD - that's how you load programs really fast. Here's what I'd do:
Pentium g630 (a dual core, but each core will be faster than an AMD core, unless the AMD chip is very heavily overclocked - ($68)
MSI B75 Mobo - ($72)
Gigabyte 7770 - ($120)
2x4gb 1333mhz RAM ($35 after promo code)
Antec One - good budget case, front panel usb 3.0 ($50)
Antec Neo Eco 450c - ($35)
Crucial m4 128GB SSD ($100)
Includes shipping. (No, I wasn't trying to hit $500 exact, lol.)
The major advantages of the build:
*The SSD - this will make the programs you put on it load really quickly, which was a bit point you mentioned
*The graphics card - while not super-powerful as graphics cards go, this system will play Diablo 3 (a relatively easy game to run) at maximum graphics settings or near-max.
*Cool & quiet - low-power CPU & GPU means that a simple budget case with even a single fan will run smoothly & you can set the fan(s) to a low speed
*You can play Diablo 3 on max settings & run your office programs within your budget (if more storage is necessary, this is still possible by replacing the SSD with an HDD).
The major disadvantages of the build:
*Hardly any storage - Diablo 3, windows\office\productivity programs, and a bunch of word & excel files will fit on 128gb - but if you have real storage needs, you're going to need to spend more to add a hard drive. This problem can only be solved by replacing the SSD (programs will load slower) with a hard drive - you can get a Seagate 2tb drive for the same price. Or by throwing more money at the computer, so that you have both an SSD & a hard drive.
*dual-core processor - for Diablo 3 and office programs (your stated purposes), this won't matter, the g630 will provide all the power you need to run smooth & fast. For something like video editing or some non Diablo 3/blizzard games, the processing power may be a bit weak. Again, really only a problem fixed by throwing more money at it ($42 to upgrade to an i3-2120, $132 for an i5-3570, or somewhere in between those two if you want to overclock an AMD quad-core).Edited by MisterFred - 8/4/12 at 1:02pm