Nothing. Once you get the 2GB back and you're back to 4, there's nothing that costs $150 or less that would be worth buying for that PC. For example a HD 4850 would be in the budget, but the improvement would be too small to be worth it. A new HDD (WD 640GB Black) would help a lot in various activities, but not so much in gaming. More RAM would be useless, with a 32bit Windows.
I'd save $100 more and then upgrade the video card to GTX 260 or HD 4870. I'm assuming that your PSU is not one of those cheap scams that claim 500W but can't really support a GTX 260, of course. What model is it?
I can't think of a game (other than Crysis) that would benefit from a better video card at that resolution. Right now, upgrading your GPU improves performance little because is now a bottleneck and upgrading your CPU makes your GPU a bottleneck. I personally have a 9800GT and the only game that doesn't play above 30fps on high settings @ 1080p is Crysis. I've played CoD4, Fallout 3, Down 2, Left 4 dead, Fry Cry 2 and The Witcher.
Since the launch of Crysis and its poor launch sales were attributes to it high system requirements I don't think we'll see anything wants that much from a system until ID's Rage comes out.
By the time your system starts lagging because your GPU can't keep up your CPU can't keep either and now you have to overhaul the whole system. Like Aevm said, nothing is worth upgrading now, and no single component is going to be worth upgrading in future either. When the time comes you'll have to replace the CPU/MOBO/GPU and probably the RAM which will cost you about $400-500 if hardware price/performance holds steady.
So I did *gasp* pretty decently on my first ever build?
Or is it so bad this is you're way of saying don't waste your money?
The games I tend to play most on my PC tend to be RTS, specifically the Total War games, which tend to be CPU governed. Since my MoBo is AM2/AM2+, would going to a triple core be worth it? I'm not really into the whole quad thing yet, as I don't really do much multi tasking.
As for the screen--- just bought this one yesterday. I've been using a 17" CRT ever since I knew what a computer was. That damn thing lasted forever. Having a screen that's wider, let alone smaller, feels weird. I guess I could always use the CRT as a dual monitor? But would going dual bottleneck my GPU during games?
But 4745454b is on to something... I could use a new desk.
Can't think of anything really. For $150... you already have 4 gigs or well have. A decent cpu that for the 150 mark wont be able to replace for a stronger one in gaming can't get another 9800GT for sli mobo ain't right could fit a 4850 or 9800GTX in there but that king of upgrade would be so minuscule wouldn't be worth it. Buy some things you make yourself feel better new keyboard mouse? speakers? another monitor as mentioned Your mobo is a G brand from ATI so you could sell your GPU see what you can get and raise your budget to get a 4870 or 260 small upgrade but but notable
You wouldn't believe the setups I've seen some people use. Milk crates, ply wood boards across bricks, sitting on buckets up side down, etc. Who wants to use an awesome computer if your butt is getting splinters?
A triple core will get you a bit more. A 9800GTX will get you a bit more. How many more bits do you need? As long as your computer is doing what you want, spend it on some things that make the experience feel better.