Try ACDSee 3.10 if you can. I was having crashing problems with the 3.1-SR1 version but plain 3.10 runs fine and is still the fastest image browser I've tried. ACDSee 9.0 wouldn't be so bad if they only listened to the users on their forum that version after version beg for an option to turn off the damn database that makes it move like a slug.
Googles Picasa2 is fairly cool and fast for being database driven, but lacks the simplicity and speed of the classic image browsers. It has the potential of real greatness.
Edit: Just tried the latest version of
XnView which is free and has improved since last I saw it. Almost as fast as I'd like it to be, and quite configurable. Worth a try if ACDSee 3.10 is not an option.