Backyard-Pool Sound System

First, check with your neighbours that they don't mind

 

You could get some outdoor rock speakers for around the pool and hang some all weather speakers on the house.

like these...

http://www.4homespeakers.com/rockspeakers.html

Problem is, we don't know your budget or layout or anything else.

Noise is a big issue (believe it or not), so the house speakers need to aim down and any others should face your house.

I've seen some really cool speakers that look like aluminum lamps and really put out some nice bass for an outdoor space, but for the life of me, I can't find the link. They double as night lighting for the pool area and don't look like speakers. Pretty elegant if done nice.