The best party music for a frat party has to include a good mix of classic rock and recent pop/rock/rap stuff. Here is a sample of good music:
CCR: Clearwater Revival Hits
Bob Dylan: Greatest Hits
The Allman Brothers Band
Phish
Dave Mathews Band
Bruce Springsteen
John Cougar Mellancamp
Def Leapord
The Mighty Mighty Bosstones
Jay Z... generic recent rap music
Threaded Mode