Ellindsey's TARDIS Tranformer is awesome. Easy to assemble, fully printable, and solid. My only complaint is... Optimus Prime? Really? With that bow tie there really is only one head that belongs there.
The hair and head snap together and hold snugly, no connectors or glue necessary and the whole thing is the right size to still allow for transforming. (In fact Ellindsey, if you could make a little more room inside the body so his head could be a little more proportional that'd be great, but if not that's okay too.)