I like the Samsung SC-X210L, SC-X300L or anything in that series. They don't make them anymore, but you can find them on ebay.
I've had a lot of problems with the all in one units and batteries freezing.
With the Samsung, you can put the Camcorder part in you jacket, with a disposable handwarmer, and the battery lasts all day. Also has an on/off, record button on the cable.
Video quality is mediocre (720x480), but no frozen batteries, and you have another camcorder to use if you disconnect the helmet cam.
You can do the same with Viosport cameras but they cost a lot more.