Intersect is a collection of common 2D collision detection tests, written as a tutorial. Hopefully this saves you from the pain of hunting them down yourself, or trying to rip them out of physics libraries.
If you're looking for further reading, you are hurting yourself if you don't buy Real-Time Collision Detection. It is easily the best purchase you could make if you are learning about collision detection. There is also an excellent list of different algorithms here.
The code is written in CoffeeScript, but it's simple and should be easily portable to your language of choice. To get started, take a look at: