BMW's official recommendation is MTF-LT-2.
The info in the DIY sticky is sourced from Mike Miller's (Roundel Tech writer) Old school BMW maint schedule. He recommends either MTF-LT-2 or Red Line MTL. Others here also vouch for Royal Purple.
Here is the relevant section from his writeup (email him for full copyrighted writeup):
"Manual Gearbox Oil: Every 30,000 miles
Only synthetic oil should be used in BMW manual gearboxes, drain interval 30,000 miles
BMW-specified factory synthetic gearbox oil is MTF-LT-2 available at the dealer, and
the spec often changes. It is a good product; I just wouldn’t leave it in service forever.
Red Line products are also highly recommended (www.redlineoil.com
All the BMW gearbox rebuilders I know use Red Line MTL exclusively, regardless of
model year or gearbox. The general consensus is MTL is the better lubricant.
However, Red Line D4ATF will require less shifter babying during cold operation. I use
Red Line MTL in manual gearboxes except where I can’t trust the driver to shift properly
when the gearbox is cold, in which case I use Red Line D4 ATF.
Red Line MT-90 as slightly higher viscosity than their MTL product, which can be useful
in reducing gearbox rattle, which can occur in neutral with the clutch pedal out in
vehicles that do not have dual mass flywheels. The rattle does not affect gearbox
function. The Getrag 280 gearbox in the E28 and E34 M5 and E24 M6 favors Red Line
BMW sequential manual gearboxes (SMG) use the same lubricant as the “real” manual –
MTF-LT-2 or Red Line MTL."