WebSphere, or at least WSAD, is a fully featured IDE and WAS is the server. IBM makes both. WebLogic is JUST the server and you'll have to develop the code and build/deploy routines elsewhere (like Eclipse or whatever).
The major difference is that WebLogic is usually 12-18 months ahead of everybody and is hands down the best app server on the planet. Conversely, WebSphere is a horribly broken product. I feel sorry for anyone (including myself) that's forced to use it. Right now I'm at version 5.1.2 and I'd say it's still beta, it crashed on my no less than 10 times today.