i used small wireless camera that I got off ebay that I use on my R/C Helicopter.. it worked ok.. i made a box for it to sit in so if wouldnt get banged of a rock hit it.. i actually never got around to mounting it on the my brush guard.. but i did take a few videos to test it.. it worked fine.. i just recorded them on my mini-dv cam on the inside of the jeep.. you just reminded me of my initial idea and i am going to get this done soon..
but depending on the quality of the video footage you want and the range of the wireless.. you can get the camera anywhere from $25-$300 on ebay is the best bet.. there is one company that really has them down pat.. i will check my bookmarks.. they were expensive but the quality was hands down awesome.. if i find one of my test runs i will post a link
EDIT: here is the link of wireless cams for r/c etc.. checkout their videos.. these are highly recommended by my friends over at rcroups.com forums..
http://www.blackwidowav.com/