FontExplorer blows DOORS off of FontBook and it is free:
http://www.linotype.com/fontexplorer
I hate Suitcase because it's autoload feature won't go away when you tell it to. Not a handy feature when you don't want it to load!
FontBook is made for the casual user. If you have more than 500 fonts I wouldn't recommend using it. I've been using FE for 2 years now without any issues and they do put out an update every 6 months or so.
Also, once you install it, make sure to run Tools/Clean System Fonts Folder so you aren't loading all your fonts there; just the required system fonts. Create a new folder called MY FONTS or something like that and put your fonts there to load.