For short puzzles, you can try out our newly launched site puzzlenode: http://puzzlenode.com/ | Only 4 problems there now but there will be at least 4 new ones added every two months, hopefully much more often than that.

These problems also serve as entrance exams for Ruby Mendicant University. We release our RMU exercises as well, but they're more open ended and likely take more than two hours in most cases: http://university.rubymendicant.com/resources/learning_mater...