I recently bought the SonyEricsson MH1 wired headset. and they work beautifully on N9 and N900.Works like a single button headset.
Remember to check for the green sony-ericsson logo. Only this works.

Reviews:
http://www.head-fi.org/t/632892/revi...st-kept-secret

Was a bit pricey(SGD 118). But if you need a good headset, then this is recommended.

Also any Iphone compatible headset can be used, with Fiio LU1/LU2 adapters, to work like a single button headset.
Already suggested earlier. I just got this one too and can confirm it works well;
The Fiio LU1 might be better option than to get a full headset that only works on the old nokia smarties.