to start you off, etronics.com is a good place to look for stuff, i ordered from them, not bad service. they ended up not having alot of the stuff in stock, but they promptly emailed me, so it wasnt that much of an inconvenience.
since you didnt say how much you were willing to spend, or what you're gonna do, i'm assuming that you dont want to spend an arm and a leg and that you're not going to slam it loud enough to shake the spark plugs out of the neighbors cars, so heres my suggestions based on what etronics has:
http://www.etronics.com/product.asp?stk_code=alpmrpf240&store=&catid=303
alpine is a good brand, this amp is really not too powerful, but it would be better than your head unit
http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=13894
onlinecarstereo.com is supposed to be good too, i havent had experiences with them, but i read it was good. anyway, this amp has more power, and not too much more expensive. kicker is a decent brand as well
http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=14322
i have a rockford fosgate amp, its alright, this one seems good for your application
you didnt say what size your speakers are, so im gonna assume 6 1/2 since thats pretty common
http://www.etronics.com/product.asp?stk_code=alpsps170a&store=&catid=358
if you get the first amp, these would be good since the wattage matches, although not necessary, its good to do that so you dont over power the speakers
http://www.etronics.com/product.asp?stk_code=jblgto626&store=&catid=358
this would also be good for any of them, the second amp would probably be best for this one
http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=13340
i have infinity speakers. the ones i have are a different speakers and theyre components, but they would be good anyway.
if you give total price range, size of speakers, what model head unit you have, and what vehicle your gonna put this stuff in, i, or someone else, could recommend other things