You should be starting with these specs and not lower
Processor: AMD Phenom II x4 series AM3 955, 960, 965, 970, 975 Processors or the intel eqivelents
Memory: 4GB of DDR3 1066 or faster (This depends on the Processor and the motherboard)
Motherboard: Gigabyte, Asus, J&W and MSI are great brands the CPU socket should be a Socket AM3 for AMD or Sockets for the intel Processors (Funny enough I dunno what sockets or Processor Intel has, there is a confusing amount of them because every Processor that is released there is a new socket) I have always used AMD just because a new socket comes every few years rather than 6 months and AMD CPU's don't change and they are cheaper. Gigabit ports, Firewire, USB 1.1/2.0, Esata, HD Audio, SATA Ports and raid controllers are pretty standard these days, also look for SATA 3 6Gbps and USB 3.0.
PSU: 500w or bigger (750w or larger for Dual/Tri/Quad SLI or Crossfire (Depends if it's a NVidia or AMD/ATI card)).
CD Drive: DVD Burner with Blu-ray reading capability SATA II Drive
Hard Drive: 1TB 7200RPM SATA II Drive
Case: your current one (if it has enough cooling otherwise Antec 900, 902 and 1200 are fantastic there are heaps of others like these)
Video Card: Depends if it is inbuilt on the motherboard you choose, Mid range cards like GT460 and GTX465 are good or any of the AMD/ATI 5000 series are good. (if you want to wait for the GTX 560 and the GTX 565 or the AMD/ATI 6950 to become cheaper) if you choose Add-on graphics card get one with PCI-E x16 2.0.
PCI cards like extra USB 3.0, Dedicated Sound Blaster, Wireless g/N, Extra USB2.0 ports and firewire and any others you may want, preferably PCI-E 2.0 if not use PCI
This is just some of what you can use, There are a lot of stuff to consider, lot of configurations to choose. Beware that AMD bulldozer is comming soon, so might wait awhile if you want. AMD again will have a new socket AMD3+ and need DDR4 Memory (First in like 3 years).