I'll second the vote for KEH. Maybe not the cheapest, but good honest folks.
Years ago I purchased a used Nikon F4 listed as very good. There was a problem w/ the meter and they immediately exchanged it for one that was absolutely mint...complete w/ box.
For new stuff.....Unique Photo in NJ is good. (I bought both my digicams from them...ask for Zack) And I like Samy's in LA. (got my Sinars and Broncolor stuff there)
Sure B&H has everything...but they can be a little snotty.