We're at a pretty cool time with technology, with Airplay we can do things that previously required lots of dedicated wiring, Crestron controllers, multizone amps, now with Airport Expresses we can distribute our audio pretty damn easily!
I've been wiring up our house with some indoor and outdoor speakers and here's some stuff I've found that is pretty cool -
Audiosource Amp-100 $100 @ Amazon, sounds good, has good power for a set of secondary speakers, and has priority input so you can hook up a radio tuner (or anything else) as your first input, but when the Airport Express kicks on, it overrides the other input.
Leviton 48211 digital volume control, $80 on eBay or $170 new - lets you add a volume control in your wall in a standard "decora" style wall switch plate; all you have to run is a cat5 to a control box you can place by the amplifier (say, in a closet)
For speakers you really have to consider what you're trying to do, how much bass you want, how big the room is, how well you want the speakers to blend into your environment aesthetically, what your budget is, you can get as ridiculous as you want.
Rob