Has anyone found a good mic for when you want to make yourself as unobtrusive as possible. I have a VideoMic Pro, but it makes the camera look more obviously like a video camera. From what I can tell the C300 doesn't apply the 1.5V to the 1/8" input so you have to have a self powered mic. I have no idea why they didn't add that simple feature, even the DSLRs have it.

I use this on my 7D and have used it once on the C300. It is very small and unobtrusive.
Sennheiser MKE 400 Shotgun Microphone

Sanken COS-11 clipped to a black camera bag and feeding into a Tascam DR-40. Easy to synch up with the camera audio if you need to, but also permits a continuous audio stream to be recorded.

I have the Sennheiser too, the MKE 400. It works well on the C300.

FWIW though, here's what I have found -> The MKE 400 on a dslr, even a big dslr like a 1DM4 or a 1D X, and the general public assumes you are shooting stills.

The MKE 400 on a C300 and many people assume you are shooting video. Even a stripped down handheld C300 w/no ext. monitor or the top handle.

As long as the mic is very small, like the MKE 400, the mitigating factor seems to be the camera.

I have a Rode Video Mic Pro that I have used with the C300 stripped down but like Brett I would still like to find a very unobtrusive mic to clip on when running without the monitor. Jim's idea of a decent lav mic to a digital recorder is nice but without some sort of mic plugged into the C300 there is no audio recorded on the camera which makes it more difficult to synch with the external audio. In this case even a very cheap'n'nasty mic is better than no mic at all. I seem to recall that years ago

I have a Rode Video Mic Pro that I have used with the C300 stripped down but like Brett I would still like to find a very unobtrusive mic to clip on when running without the monitor. Jim's idea of a decent lav mic to a digital recorder is nice but without some sort of mic plugged into the C300 there is no audio recorded on the camera which makes it more difficult to synch with the external audio. In this case even a very cheap'n'nasty mic is better than no mic at all.

I seem to recall that years ago I owned a tiny battery powered Sony mic with no cable that plugged into the mic socket of a minidisc so you could use it like a dictaphone. Something like this except battery powered would be perfect for the C300 Sony ECM-DS30P (ECMDS30P) Compact Electret Condensor Stereo Microphone (http://www.stoneaudio.co.uk/?google=10133) This should work as it is battery powered but does have a short fly lead Sony ECM719.CE7 Digital Microphone: Sony: Amazon.co.uk: Musical Instruments

Would this suit ? Tiny Mike: Ambient Recording GmbH (http://www.ambient.de/en/products/ambient-recording/microphones/tiny-mike.html)
Review here. http://www.dvuser.co.uk/content.php?CID=162

This might be useful Micro Mini Shotgun Microphones CheesyCam (http://cheesycam.com/micro-mini-shotgun-microphones/)
Would like to hear a side by side review with rode videomic and ME66 etc

Just googled it and found chad johnson done a little side by side review its here on vimeo Shootout of the Mini Shotguns! on Vimeo nice review chad, many thanks

Would this suit ? Tiny Mike: Ambient Recording GmbH (http://www.ambient.de/en/products/ambient-recording/microphones/tiny-mike.html)
Review here. DVuser: Ambient Tiny Mike ATM216 (http://www.dvuser.co.uk/content.php?CID=162)

The mic needs to be self-powered since the C300 doesn't provide mic power. So this one wouldn't work. What I really want is a small lavalier I can just stick on the C300 permanently with a short cord, which would work if the C300 had mic power. I don't know if it's possible for them to add with a firmware upgrade, but it sure would be nice.

I'm trying to avoid the shotgun as that is what makes it look like a video camera. I only plan to use it when the audio isn't critical, but would like to have ambience.

I might try the Sony ECM-719 - can be battery powered.

The mic needs to be self-powered since the C300 doesn't provide mic power. So this one wouldn't work. What I really want is a small lavalier I can just stick on the C300 permanently with a short cord, which would work if the C300 had mic power. I don't know if it's possible for them to add with a firmware upgrade, but it sure would be nice.

I'm trying to avoid the shotgun as that is what makes it look like a video camera. I only plan to use it when the audio isn't critical, but would like to have ambience.

I might try the Sony ECM-719 - can be battery powered.That's the one that I linked to earlier that has a short (couple of inches) of wire. I have a feeling that I have one knocking about in a drawer somewhere or one that looks very much like it. It could be held on with some velcro or a rubber band. It's annoying that Canon didn't build in a little mic just to provide a guide track for synchronising with an external recorder. It's a mistake that they have continued with the C100.

This has to be worth a try Tie Clip Microphone Battery Powered Mini Electret Mic 173.617 [#01776] | eBay (http://www.ebay.co.uk/itm/200827744733?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649) would need an adaptor 6.3 to 3.5mm jack plug maybe a little cable male/female? a one piece adaptor might stick out a bit too far

That's interesting. I wonder if you could get a right angle 1/4" to 1/8" adapter and then solder a mic capsule on to the end of it so it's self-contained in one unit. Might be worth a shot.