Well my 1st recommendation would be the Antec CP-850. Nothing passes it in performance according to jonnyguru and silentpcreview but unless ya got an Antec 1200, P183, P193 or DF series case, it's not gonna fit.
Here's alist I compiled about 8 months ago ....For comparison purposes , the list below contains performance ratings (10 scale) at jonnyguru.com / prices as per newegg on 02/21/2010 and ones w/ double asterisks (**) made it onto silentpcreview.com's Editor's Choice List meaning they excelled at both electronic and acoustic performance:
Antec SG-850 - 10.0 ($220) **
Antec CP-850 - 10.0 ($110) **
XFX 850W Black Edition 10.0 ($185)
Corsair HX850 850W - 10.0 ($180)
Antec TruePower Quattro (TPQ-850) - 9.5 ($150)
Corsair TX850 - 9.5 ($140)
Seasonic M12D 850W - 9.5 (NLA) **
NorthQ Giant Connector 850W - 9.5 (NFS)
Etasis ET850 - 9.5 (NLA)
Silverstone Zeus ST85ZF - 9.5 (NLA)
Enermax Revolution 85+ 850W - 9.0 ($250)
Thrmaltake Toughpower XT 850W - 8.5 ($216)
OCZ Z Series 850W - 8.5 ($200)
NorthQ Black Magic Flex 850W - 8.0 (NFS)
Coolmax CTG-850 - 8.0 (NFS)
SilverStone Decathlon DA850 - 7.5 ($230)
Enermax Galaxy DXX 850W EGX850EWL - 7.5 (NFS)
SilverStone Strider ST85F - 7.0
Silverstone Element ST85EF 850W - 6.0
NFS - Not For Sale / NLA = No Longer Available
If ya wanna check "will it do it", use the calculator here ..... the MoBo manufacturer ones seem to be a bit conservative
http://www.antec.outervision.com/