A few options:
Seperate recorder: tascam DR100, Zoom H4n etc. Another device to charge, hit record on, files to synch.
Interface device: juiced link or beachtek, adds XLR connects to your cam, some are powered (phantom) some are passive. I currently use a beachtek DSLR-5Da. I have a DXA-4 (very basic passive XLR interface with line / mic. mono stereo switching and level dials) for sale just now. This is a good match for the 5D3 as you can monitor from the camera. Your mic would need it's own power source (such as a K6 module) These generally sit underneath the camera, so are better if you don't want a big massive rig.
New Tascan DR-60D.
a combination of both, an integrated recorder and interface. You can record internally to SD, but also pump a feed to your camera. Also sits on the camera. Has phantom. Looks like being the mutts nutts.
If you want to PM me I'll give you more details about the Beachtek DXA-4 I'm selling.