i'll chime in with my 2 cents:
i'm thinking one of the s939 Opterons are basically going to be the HUGEST steal out there. the Opteron 144 in particular is a beast, especially at overclocking.
i've been doing some research and stuff and found some pretty good info. it specs out at 1.8Ghz and 1mb L2 cache and is priced around a Athlon 64 3000+ at around $160. and and overclockers have been maxing it out in the 3.0Ghz range. basically, its a FX55-57 for a fraction of the cost.
http://valid.x86-secret.com/show_oc?id=40685
http://eclipseoc.com/index.php?id=3,25,0,0,1,0