My thanks to Andrew Main for alerting me to a new source for OS X Tibetan fonts and keyboards. If you go to the downloads page on the Tibetan Geeks site and then click on the file "Monlam_bodyig-v.3-macosx.zip", you will get a set of 13 Monlam fonts and 2 keyboard layouts.
Also Jomolhari, which seems to work in 10.6 but not in 10.5.
These are a welcome addition to the two Tibetan fonts supplied by Apple and the commercial fonts available from XenoType.
Give us your impressions if you try the Monlam fonts.