There are three parts to seperates.
1. The source. Like a radio am/fm tuner or cd player
2. The pre-amplifier. This converts the low-energy signal from the source components into a higher-energey signal for the amp. It also regulates volume, and switches between source coponents.
3. The power amp. This turns the signal from the pre-amp into the watts that drive the loudspeaker.
A receiver combines a radio tuner, pre-amp & amp into one chassis. usually the parts are all cheap stuff designed to keep cost down. If you drop the radio tuner you have an 'Integrated amp' which are typically of much better build quality, and are available with more power. (Music Fidelity does have a 300-watt integrated, but its a lil' pricey).
But serious stereo geeks have all seperate components. That way you can always purchase more powerful amps, or not bother with a tuner, or whatever combination of products you want.
Crutchfield has 2-channel stereos from Sony, Onkyo, and Denon, and even a very nice denon Integrated Amp.