right now I have a mrv-f340 4 channel amp that's driving 4 infinity reference speakers. I had infinitys in my last car and have had nothing but good experiences with them.
If you have a tight budget find a special on infinity reference speakers and get 'em. They are excellent with an amp and sound really clean...You can get a good price on ebay, also I think crutchfield has them on sale too, they are relatively inexpensive.