Have to agree with Mary. You'd be hard pressed to find a better beginner cat than a Wave. But there is the danger that some may not find it exciting/challenging enough.

Hobie Europe do a few nice alternatives though - take a look at the Twixxy (terrible name I know) it's a great little trainer and has the bonus of being upgradable to twin trapeze and spinnaker! In beginner mode the mainsail can be reefed and the jib furled. With more experience you can then use the full sail area and add one or two trapezes. Finally go the whole hog and put on a spinnaker kit. Like everything Hobie it's virtually bombproof!