Lego has really done a good job with the MindStorms stuff- it's incredibly versatile (just like the original blocks).
My brother loves to do software/hardware projects for hobbies and he's got several of the kits. I collect 'robot toys' and he's given me a couple at Christmas.
To tell you the truth, though, they're not my bag. I program robots and design hardware at work and the last thing I want to do at home is the same thing. My collection is actually of 'toy robots' (like tin wind-ups) and require *much less* attention than a MindStorms kit.
MindStorms is so flexible it's like a hobby unto itself and I just don't have the time for it... but more power to you!