Adding an SSD would be a good upgrade for boot times, software load times, and map/save loading in games. A 120GB Vertex 4 or Samsung 830 would be a good buy. For graphics cards, there's not massive room for improvement there to justify the cost really. If you do replace that card, I'd go right up to a GTX670 so you have a performance gain worth spending money on. Alternatively, add another GTX570 in SLI, but be aware the performance may not be as consistent as that of a single GPU and could result in visual glitches in some games.