How do you expect to use the compass? The type of compass you need depends on the answer to that question.

>>To figure out which way is N/S/E/W: then a simple button compass will do just fine. Others have given recommendations for those.

>>To follow a bearing and/or use with a map: the a button compass is simply too primitive. Suunto makes a very nice little liquid-filled compass called the Suunto Gem. It is 30mmx54mm and has a rotating bezel and a straight edge for using with a map.