Alright, I'm going to have a little extra money in a few weeks, and figured I'd give myself a nice upgrade before I end up spending it on other things like I did a few months ago. I definitely want to get a new PSU, and am going to pick up an OEM copy of Windows 7 Home Premium (I want to keep this under $300, and the full retail version would wipe out two thirds of that alone). I figure since I'm buying a copy of 7, I might as well go with the 64-bit version so I don't need to worry about buying another copy down the road, so that means I'm getting a better CPU as well. Finally, I want a real video card, since I have a few games here that don't run so well. The most intensive is probably Doom 3 (actually, that's a lie - it's emulating GoldenEye with the Glide64 plugin). I've already browsed Newegg and picked out some hardware, but I'd like to run it past you guys to make sure I'm getting the best possible for the money I'm spending.
PSU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371023I know almost nothing about PSU's; this is part of a combo with the video card I've chosen below. Reviews make it sound pretty good; I am a bit concerned about the comments on short cords though, since I do have a fairly big tower.
CPU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103279This is the second cheapest socket AM2 CPU I saw, and the cheapest when you factor in shipping. It certainly outperforms the Sempron 3800+ I have in here now, but I have to admit I lost track of what a good processor was years ago. If I can get something better than this for about the same price, post a link.
Video Card:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150390This was the best price vs. performance video card I could find. I've never owned an ATI card though, and I've heard their drivers are garbage that actually limit the power of the cards in most cases. If you can find me an equivalent nVidia card, go for it. I have one PCI Express and one PCI Express x16 slot.
That's about $235 (with OEM Win 7). Don't drive the price up to $300 just because you can

(I'll spend some of what is leftover on RAM, and if I have any after that the rest can go towards a game or two I'd like to pick up.)