I've looked at the mbed before; while I like it for what it is, what I don't like is the "web based programming environment"; it would be a fine thing if you could host it yourself, but I don't see that as something that exists. What happens if the company behind mbed goes out of business, but you have clients or others to support? What do you do if you've built up a large codebase for some device, and there is no longer a way to compile it? These are main reasons that have turned me off of mbed...
ARM actually makes the mbed, and provides the development software. They aren't likely to go out of business!
If you want something similar with conventional development tools, look at the LPCXpresso boards:
They have the advantage of debugging facilities.