I really like my Alpine PDX-5, and a friend has the JL audio 5 channel. I think they make all sorts of 4 and 2 channel amps in the same series, but they run cool and are really small. I definitely recommend a sub, even just one 8 or 10, it's nice having the bass response. What kind of speakers are you looking at/have? Most decent amps are going to be pushing around 75 watts RMS per channel, any more most speakers won't really handle.