One of the biggest problems with the audio is auto gain control (AGC), so a mic might not get you what you're looking for.
Lots of folks are using the Zoom H4n to record externally. Haven't had one in hand yet (maybe soon), but from the specs and reports it's really solid. The built-in mics are rumored to be ok and it has 2 additional XLR+1/4" (combo) inputs and it does provide phantom power for condensers according to the specs. Have seen a couple of hot shoe mounts for them that look ok too. If you want good audio that's the direction I'd go. You can also record 4 channels of audio with it too which is fantastic. The built in stereo mic setup + 2 XLR based mics of your choice w/ real headphone monitoring ability, etc.