What's your budget? RX series speakers from Boston Acoustics would fit the bill. They go for around $125 a pair and can work well with both head unit and amp power. But you really want to decide ahead of time what you want to have so you don't waste money. I know to many people who got something and then wanted more and then more and in the end spent 3x the amount they should have to get to the point they finished. Ask yourself, do I want a sub? How loud do I want the music to be and be clear? How important and often do I use the sterio and the car? What do I feel comfortable spending? Does this include me doing the install or paying someone to do it for me?
BTW, the site talking about the speakers is at
http://www.bostonacoustics.com
and the site selling them is
http://www.tms-electronics.com