I have the HF 100 and have used lavs and, other microphones by means of an interface. The one I have is the XLR2.
BeachTek also makes one. There are a couple different models by different makers. It will handle 2 inputs, mic or line and 2 1/8" aux ins. There is a mono/stereo switch, a mic/line switch and a ground flip. If you hunt around on ebay, you can find them. There is a current listing for about $40.00. You MUST use dynamic mics or electret condensermics that will supply there own power. I got very good results by plugging in my Rode NT4 (with battery) into the interface and then the interface that attaches to the bottom of the camera and on top of the tripod.
I have tried 4 external microphones for my Canon HF100 and only one of them works (that being that from my son's singstar playstation game!!).
I'd bought a Sony Lavalier microphone especially to use with this (which doesn't work). Are there certain microphones that do and don't work? Is there perhaps a problem with my camcorder input?
What would be a relatively cheap solution to a wired lavalier microphone that you might recommend?