If you took that rig right there, and made some tweaks, you could get some stuff that would give you a pretty reasonable rig right now.
Keep the case: $40
Keep power supply: $45
Keep the processor: $125
That's $210 right there.
I'd sub the motherboard for
ASRock B75 PRO3-M LGA 1155 Intel - $65 (+ 17): This would allow you upgrade RAM later on.
Sub the RAM for
8GB (2 x 4GB) 240-Pin DDR3 - $80 (+ 50): 4GB of RAM won't get you anywhere for gaming and most stuff. 8gb is where it's at.
Upgrade the HDD to
1TB Western Digital - $60 (same price!): There's not much point to getting a lower GB HDD, unless it's super cheap. If you upgrade to an SSD later, you can just switch the HDD to backup/media/extra games and apps.
That right there is $415 without a graphics card. Now, you can keep that $90 card to push it up to $505, which would still give you a pretty good gaming rig with much less waste in the future. The first thing I'd target for upgrade would be the graphics card, because that'll do most of the heavy lifting. Though if sound quality were a thing, you could also drop in a Sound Blaster X-Fi for pretty cheap. Further in the future you could grab another 8gb of RAM to bring it up to 16gb, replace your disk drive with an SDD (while still keeping the HDD!), and even bump the processor up to an i7 for the amount of processing power than a gaming rig will need for probably half a decade or more.
With that, if you replace the CPU/Graphics Card, you could pick up other, cheaper parts to build a pretty reliable HTPC/Home server.