I'm eventually going to toss some upgrades into my computer here soon and wanted to start my search with some suggestions as to what you all think needs to be upgraded first (i.e. weakest to strongest)
First, I'd recommend replacing that power supply. Not sure who told you that you needed a 1000 watt PSU for a single graphics card system, but you don't and it's not likely you even need one for a Crossfire/SLI set up. A quality (Antec, Seasonic, PC Power and Cooling, Corsair, FSP Fortran Source) 650 power supply would be sufficient for any single card system. I'd probably be looking at a 750-850 watt PSU (again from a reputable manufacturer) for an SLI/Crossfire set up.
Next, I'd look at adding an SSD for your OS and programs. It doesn't need to be huge. I think a good 120GB SSD is more than enough for the OS and programs/games. Anything else that needs storage can go on your green drive.
Third, since you're a gamer, would be the graphics card. I'm not one to upgrade a component just because I can. You're current graphics card is plenty for your needs. If you're interested in an SLI configuration and you can find a deal on another GTX 470, that and an appropriate power supply might be ideal. Otherwise, if you're looking for a multi-monitor configuration, then the PSU and Graphic Cards should probably all be upgraded.
Finally, would be the core system. Again, I don't see these components as needing an upgrade; i.e. the improvements are not worth the cost. Further on down the line, sure, but I'm talking another generation or two of Intel Processors.