Two good over the counter car soaps are Meg's Gold Class (which was mentioned) and Megs NXT car wash (smells great). As mentioned - whatever you do - don't use Dawn!!! It will strip whatever wax/sealant you have on your car and leave the paint unprotected. Bird bombs and acid rain will etch right into the paint.
You should be using two buckets - one for washing and one for rinsing.
Make you you follow the directions in terms of dilution ratios. Most any car soap if mixed at a strong enough dilution ration will strip the paint - and that's exactly what you don't want.
Use a good quality waffle weave towel to dry and mist the paint with quick detailer before drying.
Read and learn. One of the best detailers in the country:
http://www.detailedimage.com/Ask-a-P...-pearl-part-1/
I'm not at all pushing the products they sell as I know Adam's is a sponsor here. Detailing is WAY more about technique than product.