A nice choice would be PIC18 by Microchip
It has quite alot of material, documentation, tutorials and projects on the internet
Free IDE and compiler.
you can pull your own flash writer in a few minutes.
(Although for a debugger to work you'll need to work harder)
If you're a student (or has a student email address) Microchip will send you free sample chips. So basically you can have a full development environment for close to nothing.
PICs are quite prevalent in the industry. Specifically as controllers for robots for some reason although they can do so much more.
