Consider carefully what games you'd wanna play and how much time you'll spend. In some cases (like me), I went for a high spec rig but I didn't have much time playing since I have work; so hindi sulit.
Also, don't neglect your monitor, a cheap small monitor 15-18" is a lot different from a good large widescreen ~14", difference in graphics quality. Make sure you don't get a keyboard that's rigid on the keys. Carefully balance your budget.
As for your homework, tom's hardware is good place.
this is the same reason why I stopped playing and building gaming rigs..
money and time..
pag isipan mo muna mga games na lalaruin mo.. and yung result na gusto mong makita..
with those elements mas madadalian ka mag isip ng pwede mong gawing build.
pwede kang mag AMD (APUs or CPU) or Intel..
video card.. I don't think you can build a highend gaming rig with a great video card at 18k
so tulad nga ng naka saad sa taas.. i consider mo ulit yung games and expectations mo.
you can build an APU w/ a crossfire stuff. it's a decent and budget "gaming" unit but I don't really think it can run the most demanding games of today on ultra high. go and check it out. baka maka tulong sayo yan.