For me personally I like to buy high end business class OEM towers used and upgrade them.
For example I have:
Dell Optiplex 745
2.4 Core2Duo
2gb ram
250gb Barracuda
Ati HD4650 1gb OCd
Asus Xonard DG PCI soundcard
total cost after selling old system parts
is $75
WinTV USB TV tuner - $5 yard sale
HP Laser All in one Black and White printer - $35 secondhand store
HP Officejet All in one w/ card reader - $0 supposedly broken
Viewsonic 22inch 1080p HD 2ms response - $90 Used came with DVI
Samsung Syncmaster LCD secondary display - $40
Creative T4400 surround sound - Free on Craigslist
total cost for everything - $245
system works nice
Great office system
mainly MSoffice,photoshop,multimedia and light gaming system
BUT I wouldnt buy a brand new budget or high end OEM since they lose value quickly
if I wanted to go all out I would build my own