I use the BH-604 on my N900.
The only downside about this headset is that it's much bigger than all other headsets in this thread
(IMO this is not a downside but i guess some of you would like it smaller)

Soundquality is simply amazing.
Crystal clear sound and a warm beep bass!
and it's realy pleasurable to have this on your head because it's so soft.

The battery lasts over a week when i use it every day 2-4 houres

here in belgium it costs €90. Wich imo is waaaaaaaay to cheap for this headset