OpenEmu is a new, sweet looking multi console emulator for macs. Organizes roms by system in an iTunes style and automatically downloads cover art for every game. Well, at least the (U)(!) goodroms. Hacks and trainers (or bad dumps) don't automatically do that. I think it matches by rom checksum rather than filename. It also has a selection of filters to apply. My favorite is the NTSC one which captures the scan lines, color bleed, and shimmering of an old 80s tv perfectly.
I really like it so far. The only thing I still want added to it is support for either a cheat database or the ability to save cheats you manually enter.