BrainPOP ESL is a one-stop shop for all beginners to intermediate students of English. It caters to the elementary classroom but the content of the lessons, the contextualized language, humor and wide breadth that it covers is quite remarkable. I think it is what many other progrmas and sites have attempted to achieve, but have fallen short.
The problem is that it is all Flash -based so no luck for the iThingy crowd, although an iOS app is available–with limited content. The good news is that it only promises to get better, and new levels are being developed.