I'm using the Zoom H4; not the new model, the zoom H4n with my 5d2. The quality is excellent. I've had syncing issues and it's slowed down my production and got in the way of my creativity -- especially since I don't yet have a budget for post production and sound assistants. Many people online are successfully using the h4n to input directly into the 5d2s. You gan get around the external gain control by using software called Magic Lantern.
I'm trying this approach; I hope to get the correct patch cables this week. If this approach works, I will use a offshoe flash bracket to mount the zoom h4 when using with the camera so I can simultaneously take stills. Do let me know if you'd like me to report on my success.
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.