Outdoor speakers with solid bass

A buddy asked me to research speakers for use outdoors. He does have a nice system in the living room, so knows the difference between good and bad sound. His concerns are getting adequate bass and the speakers being able to withstand the elements. It's California, so the latter is mostly just rain, wind and sun.

I've looked at what is available via the Internet and wanted to get you input, too.

Budget is in the neighborhood of $600 give or take a hundred or two.