I wrote a tutorial for ActiveTuts+ (previously known as FlashTuts+) about parallax scrolling, an effect you can use to make 2D games appear to have more depth. You can see the effect in the little demo above.
Click here to check the tutorial out.
Actually, it explains a few more things beyond the parallax effect, like how to make your game’s “camera” (or “viewport”) appear to follow the player, and how to create infinitely repeating backgrounds á la Scooby Doo
It’s pretty long, so I tried to lay it out in such a way that you don’t have to read the whole thing to benefit from it. For example, you only have to read the first half or so in order to understand how to make a side-scroller.
I’ll be following the comments there in the same way that I follow comments on my own blog, so if you have any questions, please post them over on ActiveTuts+.
And if you make anything cool with the effect, I would love to see it