ok i got a few answers.
10K drives IMO are over rated, they are only necessary for high performace rigs, like a 4Ghz overclocked e8400 with 3GB RAM ann a 8800.
for general use and normal gaming 7200 rpm drive are perfectly capable.
ok RAM DDR3 is out but again i dont think the hefty price tags are worth it, it may not be the best RAM out or the fastest but definately the best price/performacne ratio is still DDR2 800Mhz, you can pick 2Gb up for as little as £30 or $60 probably $50 actually, and again DDR3 is only worth the extra in the high end gaming rigs, and even then the high timings still put me off.
ok for a powerful rig with say a e8400/Q6600 with say 3 hardrive 2 DVD drives a high end motherboard, 4 sticks of DDR2 RAM and an 8800GT id say a decent 650Watt or maybe a 700 to be sure.
ok a nice 20" or bigger monitor well thats debatable,
someone like me wants a big monitor with a viewable resolution that looks nice, someone else on the other hand would like a big monitor with a big recolution with great response times etc, i dont care about that stuff.
with all honesty when buying my monitor i went for the cheapest 22" monitor with a brand name, thats it. so ill reccomend 1 like me.
20" - http://www.ebuyer.com/product/143960
22" - http://www.ebuyer.com/product/143051
1 thing i will mention is none of those have DVI.
if you want a good response time monitor with high spec then im not your man wait till someone else posts