Tons of free indie games
DigiPen Institute of Technology is a dedicated leader in education and research in computer interactive technologies. Every year, students from DigiPen Institute of Technology come together to create dozens (if not hundreds!) of high-quality, original PC video games as part of their course curriculum. Each games is posted on the DigiPen Game Gallery for the whole world to see, and the very best are submitted to international game festivals to compete against other student-made games. Download the games http://games.digipen.edu/ Enjoy :)
Some interesting looking games there, but overwhelmingly biased towards sideways platformers.
I am going to poke through the Poetic section
They have all kind of games, not only sidescrollers and platformers, You'll find, FPS, Adventure, Puzzles, and others without a clasification taditional. For example the game Narbucular Drop is a precursor of PORTAL