Obviously, one of the best places to start looking is mousesavers.com as has been mentioned.
I found that one of the lowest pricing codes for my dates was AWD K199060 used with
Avis. That would price out a compact for $230 for 8 days (including tax). Much better than most other rates I've found.
I also found that the Marriott rate with Hertz was very good (that's what we're using). You have to be a member of Marriott's loyalty club, but it's free to join. I used their CDP#154080 and one of these coupons:
Economy - Full-Size
* Save $15 and double points on weekend rentals (PC#119792)
* Save $25 and triple points on weekly rentals (PC#119825)
Premium or Larger (including Prestige, Fun or Green vehicles)
* Save $20 and double points on weekend rentals (PC#119781)
* Save $30 and triple points on weekly rentals (PC#119814)
It's good until December 31, 2008, however you should be aware that Hertz is off-site. We just took the shuttle and it really took very little extra time, and for the savings we're getting, it was well worth it.
Good luck!