I'm using Head Direct RE0.

http://www.head-fi.org/products/head...phones/reviews

They cost 80$, and they have, IMHO, the best sound you could get for their price range, and are a good match for the N900. Their sound is very natural and very transparent, and don't add anything to the sound or take away from it.

Not for bass-heads, but great for people who care about clarity and detail.