One thing to always try out in a store, when you comparison shop for speakers is their efficiency. Rather than have to buy a monster power amp to drive a set of low efficiency speakers, just set up a test CD into a powered mixer, and start plugging in different speakers without touching ANYTHING.

You'd be amazed at how much difference in volume different speakers, even ones from the same manufacturer, put out given the same power IN...

All other things being equal, efficient speakers will save you a fortune in high power amps, and these are usually the heaviest thing to lug around...