I got a mag mount from Byonics (http://www.byonics.com/mt-antennas
) which worked great until I got it caught in the garage door
My current 2M/440 mag mount cost $30 from HRO and works well and is much sturdier.
You can also get a NMO or UHF mag mount base and attach whatever antenna you have to it. Some work better than others in a mag mount base, however.
Best advice? shop around on their site.