This is probably a very open ended question but, in terms of a gaming pc, with what mobo, prossessor, and Graphics card will get you the most performance for what you pay. What Combonation of the above components would give the best performance whilst still keeping withing a reasonable budget.
Any motherboard with the nForce 4 chipset is generally a good choice. If you want overclocking, DFI is probaby your best choice, followed by Asus. Epox may also be something you want to look into as their 9NPA+ boards don't seem to have any issues outside of what any other motherboard runs into. If overclocking isn't a priority, Gigabyte or Foxconn seem to have some nicely priced boards with a good value package. Get a board with PCIe x16 slots. While you may not use it, a motherboard with an SLI chipset can be had for a reasonable cost, so it may not be a bad investment for a life extension down the road. Until Conroe (Core 2 line) hits, you're better off to stick with AMD. A 3000+ to 3500+ are a good value right now (approx. $90-140US), particularly in the Socket 939 department. The CPU is important, but gaming isn't going to be as affected nearly as much by the CPU speed as skimping on the video card. If you need to cut corners, cut it with the CPU speed. RAM: 512MB is the absolute lowest you want to go, but given the cost of a good 1GB easily below $100 (US), this is the sweet spot on the low-end. Depending on the kit target, 2GB isn't terribly priced either, but not absolutely necessary. If you play (or want to play) Oblivion or FEAR, I'd certainly recommend considering 2GB. For everything else, 1GB will do the job. Video card: A Radeon X700 or X1600Pro or GeForce 6600GT is around $100US, and that's where I'd start. The middle of the road values inclued the GeForce 6800 and 7600GT (the GS is comparable to the 6600GT FYI, and costs a little more) on the nVidia side and the Radeon X800/X850's on the ATi side. Power supply: This is where you don't want to go to cheap on, since it can make or break a system in the stability department. SLI Certified power supplies are a fairly safe bet, but do not confuse them with SLI Ready ones. SLI ready simply means they have 2 PCIe power connectors. SLI Certified units have been tested and approved by nVidia for use in SLI power boxes. You're looking anywhere from $70-100 US, and something around 500W. Wattage isn't the only thing to go by, and my entire dissertation is linked in my sig.
a mobo with the nforce 4 chipset coupled with an amd athlon 64 processor and an nVidia gfx card should give you the best value at the moment