samsung is a good brand. also a lot of people are going for acer monitors these days. their on the cheap end but seem to work fine. other than that i wouldnt upgrade till the core i7's come out along with cheaper mobo's for them.
Replacing the video card would be silly too, since the GTX 260 is still one of the best. You'd spend $500 for a HD 4870X2 or $450 for a GTX 280 but the improvement wouldn't be worth anywhere near that much.
Adding a second GTX 260 is probably the best thing you can do, considering your SLI motherboard. It would make a difference in Crysis at 1680x1050. Not really needed elsewhere IMO. However, the 650TX is not powerful enough for all that. If you like this idea, get an Antec 850W or a Corsair 1000W. Check this out: http://www.slizone.com/object/slizone_build_psu.html
Maybe you should just get some nicer speakers, or more HDD space.