My first clipless pedals were the platform/SPD pedals. I liked the idea of them, but found that I never actually used the platform part. The pedals were overall kind of heavy, so I switched to ones similar to these: http://bike.shimano.com/publish/cont..._mountain.html Also onesided, with sort of a platform. I really like them, but I always seem to be searching for the right side to clip in. I guess the part where you clip in is heavier and ends up at the bottom. I think for my next ones I will go double sided for that reason.

Sorry if you already know all this, but give yourself time to get used to the pedals, ride slowly in the empty parking lot or on grass. And if you normally don't wear a helmet, wear it, you may forget you're clipped in and fall.
When you're buying your cleats, get multi release, not the single release ones. They're easier on the knees and easier to get out of. And set your tension low, at least at first.
Good luck, I love my clipless pedals, couldn't do without them.