I used to have the $30 Verizon universal mini-USB car charger, and it was crap. My TP1 would take too long to charge, and would give me feedback on my stock car stereo system (I mention it's stock in case someone wants to suggest I have an amp with a bad ground). Anyways, I returned that junk, and bought an official HTC car charger which is AWESOME! It charges at 2A, it's official HTC product, looks really nice (with a blue HTC lit logo). I highly recommend it. I bought it for ~ $20 from an Expansys.com about 1 year ago.
http://www.expansys-usa.com/p.aspx?i=169461. Again, if you're going to get a car charger, I HIGHLY recommend this one.