What's a clean/simple way to do side-scroller collision?

[Fourex]

I'm experimenting with a side-scrolling game. I can't figure out a good way to check when my main character is running into walls, or on the ground. I need a way to check if he is hitting his left, right, bottom, and top sides. Does anyone know of any tutorials, or examples? It doesn't really need to be for Love specifically, I just need a basic method. Thanks in advance!

[bmelts]

http://www.metanetsoftware.com/technique/tutorialA.html

[Fourex]

Thanks!

EDIT: Woah, this, and the other tutorials on that blog, are basically everything I will ever need to know for platformer collisions...