We've featured one DIY MacBook Tablet before, but this particular model takes a very different approach, modding only the screen itself for a cheap, usable tablet computer.
Unlike most custom Mac tablets, this mod doesn't include any extra parts besides the touchscreen itself, which hacker Enigma-penguin got for around $100. The computer doesn't have a swivelling screen or anything like that - it's just a backwards-facing touchscreen, accessible by cutting off most of the lid.
Obviously, it's still a pretty heavy mod, and the project isn't for the faint of heart. It costs quite a bit less than other similar projects, though, so if you were disappointed by the iPad, it's probably the most accessible Mac tablet mod out there. It's still a work in progress, but only needs a few more touches and looks pretty usable in most situations. Hit the link to read up on the full project.