Looking at a system for $1500 or less for gaming and/or video/graphics processing and rendering?
If going with Intel, go with an i5 2500/K (3.3GHz 4 core/4 thread) or i7 2600/K (3.4GHz, 4 core/8 thread) on the Sandy Bridge LGA 1155 platform (the K series are unlocked multipliers for overclocking, provided the board is capable of handling it, and have an Intel HD Graphics 3000 built into it compared to the Intel HD Graphics 2000 in the non-K chips).
Look for a H67/P67 (can't use the GPU side of the chip) or Z68 (CAN use the GPU side of the ship) motherboard (avoid the H61/65 boards and anything labeled M-ATX/uATM (Micro ATX) or ITX as those are smaller than a regular ATX board and generally cut down the RAM slots from 4 to 2) like the plague) and check if it'll max out at a minimum of 16GB with 4x double-sided 4GB DDR3 chips (I got burnt with a HA65 (H61 sub-type) from Gigabyte that "could" do 16GB with 4x single-sided 4GB 1333MHz DDR3 chips, but practically tops at 8GB with only 2x 4GB double-sided chips or 4x 2GB single-sided chips, as 4GB single-sided chips are pretty much non-existent in Aus)) and have installed a minimum of 8GB (either as a pair of 4GB chips or two pairs of 2GB chips) as you WILL need more than "just" 4GB if running Win7 (64-bit only. 32-bit is useless if you want more than around 3.5GB of usable RAM), even if you have a "2GB" video card in the PCI-E slot.
I haven't got much advice for AMD if you're going that route, beyond the same checking for 4x 4GB double-sided chips for a minimum of 16GB and load 8GB for the initial build, and go for the Black Edition AM3 chips if you're planning on overclocking and trying to squeeze more processing performance out of the CPU in exchange for a (theoretically) shorter life span of the chip.
I have no brand loyalty to either Nvidia or AMD/ATI when it comes to expansion cards, but remember a uber-powerful graphics card doesn't always mean best performance and will shrink the cash in the budget for the rest of the components (chassis, hard drive, optical drive, monitor, keyboard, mouse, power supply). I suggest ASUS and/or EVGA as I've found they tend to provide the best support, warranties and drivers.
A 550-650W PSU is pretty much the low-end for power supplies these days, with video cards having heavier power requirements than they used to. Going for a 750W should keep you fine if you dual-card (SLI or CrossFire) your rig. I'd recommend Thermaltake in this regards, particularly their modular PSU line of EVO Blues (can add/remove power lines for SATA, Molex and PCI-E power as needed upon the build, reduce wastes energy and improve internal airflow), though any decent modular PSU should do.
Hard Drives, I suggest keeping away from Western Digital and checking Seagate or Samsung instead. a 1TB drive split into 2 or 3 partitions is basically the minimum, as anything below a 500GB drive (or partition) can and will be chewed up quickly with the more stuff you install and save to it. *speaking from experience of ~JUST~ getting along with a 200GB Seagate Barracuda atm and planing on tossing in a 1TB drive ASAP for data storage and processing.*
Optical drives, a DVD ±R/RW drive is pretty much the standard these days, if you can get a Blu-Ray player/recorder that does DVD ±R/RW, then go ahead. I generally recommend ASUS though.
Keyboard/Mouse, any brand oughta do for these two items, though I generally recommend Logitech for best driver support and durability (still running a 10 or 11 year old wireless keyboard/mouse combo from Logitech that I've had little problems with).
Monitor, I wouldn't recommend anything below a 19" or 20" (apart from laptops) and suggest getting one that does 1920*1200 (8:5/16:10) over a 1920*1080 as the 120 extra pixels of depth is another 230,400 pixels of viewable and usable space, something one shouldn't under-estimate.
Chassis, get what ever you want, just make sure it'll fit the board you are looking at (ATX is the standard size, some board makers make the board longer/deeper than usual, mostly for providing extra PCI-E slots or other plugs and headers (say, more than 6 SATA drives or 4 USB headers instead of the usual 2), so keep in mind the length/width of the board and it's type name, such as E-ATX or XL-ATX), along with all the part inside (hard drive/s, optical drive/s, PSU, video cards).
There are some cases of 'overkill' when it comes to chassis/PSU and board/GPU matching (eg: a CoolerMaster HAF-X (942) with an ASUS P8H67-V3 and Nvidia G210 and 1000W PSU), so don't be afraid to down-size the chassis unless you plan on things that the bigger chassis can do that might not be possible with a smaller chassis (lots of watercooling if you're gonna be overclocking the guts out of the system for example, but for a $1500 system, that's unlikely).
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Whoo, I think I got everything there, though I skipped the OS and software as YOU know what you want to use there, so beyond my pointing out to get the 64-bit version of the OS, there's not much else I can say there.