If you can take somewhat lower quality:
LiveSynth pro & sYnerGiGS Soundfonts
LiveSynth Pro & SGM180 GM Soundfonts, Papelmedia or Titanic

Higher quality but slow loading:
Colossus
Bandstand (will be updated to improve loading times, etc.)

[This message has been edited by Frank L. Rosenthal (edited 06-28-2006).]