Cameras usually have 10 or 12 and that's enough for most people. You probably won't need more than 6 unless you're making huge prints.
Instead of just thinking about megapixels, look for other specs in a camera because megapixels really aren't important. They're mostly just a gimmick unless you really need them.
Read about the megapixel myth here: http://www.kenrockwell.com/tech/mpmyth.htm