Neither the GH1 or the 7D has good audio capability so external devices is a must.
I've looked a lot on different solutions for audio recording and bit by bit it falls into place.
Several factors were important to me. Portable, clean sound, easy to use and not to expensive.
I like the sound of a shotgun mic more so than a lavalier mic. I tried a cheap shotgun ($35) and the sound quality was
ok but construction quality another thing. The first time I removed the XLR cable the whole bottom part came loose!
After some soldering and putting in a beefier cable it works again but I do not trust this one. Instead I settled on an
Audio Technica AT897.
It's a shotgun mic with really good rejection and low noise. You can power it in several ways. AA battery, 48V or even 12V will work.
It's also smaller than the cheapo mic I first got. Price including shipping was $240.
I have a
Sony PCM-D50 which I wanted more than the Zoom H4N which is very popular. D50 is cleaner sounding and has a really good limiter so sound quality
was the deciding factor. It's a solid piece and runs really long on the batteries. Prices from $400.
A small headphone and foldable to fit in my backpack steered me towards
Sony MDK-V300.
They get the job done are foldable and are light on the head..

The next step is to try out a Juicedlink CX231 ($299) connected to either camera.
I'm eagerly awaiting the Magic Lantern firmware for the 7D.