Two or three times a year Steam hosts a Next Fest, where every developer and their mom posts a demo of an upcoming or in-development game. They're awesome, generally speaking, ranging from fantastically broken and hysterically bad to outrageously good and perfectly polished.
During Next Fest you can almost always find some indie gem or discover that a mid-tier game is going to be way better than you'd ever expected. They're also a great snapshot into the development process—one that you used to only get by attending big expensive game shows like PAX or Gamescom or Tokyo Game Show.
