The sleekest looking cabinets, in bathrooms or elsewhere, are the ones that are built-into the wall. This allows the cabinet to be almost flush with the wall, rather than sticking out by three, four, or more inches. In a bathroom, the effect is a more modern look than regular medicine cabinet would provide, while still providing plenty of room for medicine and toiletries. These are available in mirrored and non-mirrored versions.
Here’s a model that doesn’t look too bad:
Recessed medicine cabinet without mirror pictured: Broan-Nutone Unfinished Wood Louver Door Polystyrene Body 16W x 22H in. Medicine Cabinet 607ADJ
I prefer the retro look of these:
Left: (WC-418) Solid Wood In the Wall Bathroom Recessed Medicine Cabinet, Your choice of Enamel Finish, 4″ Deep, mounts in wall using only construction adhesive by WG WOOD GROUP
Right: (WC-430ws), 30″h Recessed in wall bathroom medicine cabinet, with shelf, solid wood by WG WOOD GROUP