I liked three brothers racing in costa mesa CA, I bought a XR600 from them. The only thing I didn't like is you have to pay doc fees, and taxes right there. ( same at all dealers.)
If you look on
www.ocautotrader.com then click on cycle trader they'll give you all there bikes listed online, several dealers have there links listed for there entire used inventory. Another resouce is
www.cycletrader.com. for nationwide results.
Do you know what your looking for 4 stroke or 2 stroke? how new? or how much $$ your willing to spend?
I know 3 bros. has 5-10 used bikes that look pretty good,
champion has a couple yz400's I saw yesterday,
I also know some quality friends selling 2 stroke and 4 stroke bikes.
I may be selling my KLX340 4 stoke w/ cust susp. , with a new rebuilt motor (being done at Mission Yamaha currently) if I can work out a deal on a 2002 yz250f.
Let me know what your looking for, I might be able to steer you in the right direction. Looking forgood deals on new bikes is kind of a hobby for me.