6.002x is an amazing course (it's the only EdX course that has run so far, but they have a great platform).
The Udacity courses are generally slightly easier (e.g. they avoid the low-level details of the maths), but I really enjoyed CS373 (Programming a Robotic Car) and CS212 (Design of Computer Programs).
The Coursera courses are a little hit and miss in terms of quality, but Quantum Computing and Design and Analysis of Algorithms are both very good.
The Udacity courses are generally slightly easier (e.g. they avoid the low-level details of the maths), but I really enjoyed CS373 (Programming a Robotic Car) and CS212 (Design of Computer Programs).
The Coursera courses are a little hit and miss in terms of quality, but Quantum Computing and Design and Analysis of Algorithms are both very good.