Microcenter runs extremely good deals on Intel CPUs, but everything else is more expensive. However, you can't buy online, so if you're not near one, it doesn't mean anything.
@Jcomps: Doesn't matter. OP isn't near a Microcenter. Also, I wouldn't touch the 570 when you could get the 5970 into the build. Or the Storm Scout (overpriced) or OCZ PSU (lower quality) for that matter.
@OP: You'll be fine with a GPU upgrade with an AM3 board as long as you don't go with a nVidia GPU. AMD (who owns ATI) doesn't natively support SLI (nVidia's dual card technology), so if you were to get a nVidia card, they only upgrade path you'd have is replacement.
The only potential issue with the AM3 socket (and LGA1156 as well) is that the boards are basically limited to 8x/8x speeds with Crossfire/SLI setups. Full speed is 16x/16x. However, it's not a big problem, as that typically translates to a loss of under 3% performance (over an unrestriced setup) even when using the 5970. If you use a lesser card, that goes down as well.
The bigger issue is that the best CPUs on either socket right now can't keep up with Crossfired 5970s. However, it's also not an issue because no CPU can, and it's so massively powerful already that a little bottlenecking isn't noticeable.
An AMD build would give you the most potential for upgrading later. I'd say it's even better than an Intel build. With an AM3 build, you can get the ability to add a second GPU (non-nVidia of course), add SATA III/USB 3 devices, and drop in a brand new CPU (either the X6 hex-cores or Bulldozer). With an Intel build (LGA1156 specifically), you only get the added card and the SATA/USB. You completely lose out on any CPU upgrade, which could cost you a couple of years of use later on in the build's life.
I see the upgrade path for an AMD build like this:
First 3 years: No changes needed, or possibly a SATA III SSD
4th year: Add second GPU for cheap
5th or 6th year: Upgrade CPU to the highest possible
Late 7th year: Replace build
Intel's upgrade path looks like this:
First 3 years: No changes needed, or possibly a SATA III SSD
4th year: Add second GPU for cheap
Late 5th year: Replace build
An AM3 build will also last you for years without needing to be upgraded, but that's true with pretty much any $1,000.