Processor: Anything duo core and above, Intel not AMD. Remember, very little software supports the quad core. At least 2.4 Ghz 3.0 is better.
Video: Nvidia for sure, 8800 GT if you can afford it or the new 9 series which are also pretty good...avoid ATI like the plague
RAM: 2 GB minimum unless you run Vista then you had better have 4. OCZ and Corsair are good brands.
HDD: As big as you can afford, I recommend Western Digital.
Monitor: At least 19" 1000:1 contrast ratio 5 ms access time. This is the low end.
PSU: At least 650 watt, unless you want to run SLI, then you may need more.
MB: I like EVGA (for video cards as well), but as long as you get the 680i chipset your OK. You can get the 780i if you have money to burn but it's not necessary.
Case: A matter of personal preference, but the Antec 900 and 1200 are awesome cooling machines.
Mouse: Again, a matter of personal preference, but I like the Logitech G5 (an upgrade from the MX518).
If you have any other questions let me know.
Smurf