So I've been thinking about upgrading this computer I built a little while back. It's pretty good right now, so I don't think the upgrade will be for a while, but when prices drop on some newer components.
Right now I'm running a Phenom II 3.0 Ghz Quad core CPU w/ stock cooler, 512 MB Radeon 4850 GPU, Gigabyte 770 northbridge MOBO with 1 PCIe x16 slot, 4GB DDR3 1600 RAM, and all of it stuffed in an Antec VSK-2000 with all the fan slots filled.
Things I've been thinking of doing:
Upgrade HDD to 60-64 GB SSD boot drive. $150-$250
Upgrade to 5850 (maybe 5870) graphics. $250-$370
Upgrade to new motherboard for chipset, USB 3.0, SATA 3, eSATA port, and more PCIe x16 to allow other upgrades. $150
2x 4850 graphics or 2x 5770. $100-$350
new six core phenom II 2.8 Ghz-3.2 Ghz (read in a review that both are exactly the same, just overclock 2.8 to 3.2 and save $$, not sure though). $250-$300
Get 4 GB more RAM, DDR3 1600. $100
Upgrade case to Antec 300 (except Eric also has the 300...) or CoolerMaster RC 690 for more cooling, room, and looking better. $60-$80
Upgrade CPU cooler and overclock it. $30-$60
Looking for the one that will make the biggest difference.
The best choice depends on what kind of improvement you want.
If you want better performance in gaming, you should look at improving your graphics setup first. Your Phenom II X4 shouldn't be bottle-necked by a Radeon HD 4850; an HD 5850 is a much better match for a Phenom II X4. Two HD 4850s in crossfire would be comparable in performance to an HD 5850 and cheaper to set up, all things considered. Down the road, though, the HD 5850 will show its edge in DX11 games.
If you want more processing power, get a CPU cooler and overclock higher. You should be able to get quite a bit more performance out of your Phenom II X4. The Cooler Master Hyper 212+ is the best value around.
Only if you use really processor intensive, well threaded applications (not just gaming, browsing, productivity), should you consider upgrading to a six core Phenom II or 8GB of ram.
An SSD will give you the obvious benefits of faster start-ups, shutdowns, loading times, and file transfers, but it won't improve gaming performance noticeably.
I don't see the point in upgrading your case unless you want to get something really high end. The differences between the Antec 300 and VSK-2000 aren't really big enough in my opinion to warrant upgrading (especially if you already have yours filled with fans). Your setup doesn't really need a top of the line cooling setup yet, either.
Best upgrades alternative for you is only the SSD
I prefer wait untill AMD Buldozer, Intel Sandy bridge and AMD/ATI HD6000 comes to market for upgrading the proc, RAM and/or GPU.
You might wanna get the new ones or enjoy the price cut on todays components.