Look for a Yaesu FTM10SR
The radio I just put in my Jeep was originally designed for mounting on a motorcycle...
The Yaesu FTM-10SR
Completely water proof, shock resistant housing.
Head is designed to mount to the handle bars and works as the mic too.
They were discontinued last year for a new 50 watt version... the 10SR is only 10 watts... but enough for reaching most repeaters in urban areas.
They had great close out deals on them including the hand held mic just last spring... you should still be able to find one on one of the Ham web sites.