As a summer project I decided it would be fun to make a flash game. Right now I'm going for something like the look of http://www.terraria.org/. It's been a lot of fun, but today I've hit a snag. I need a way to generate my worlds. I've read up Perlin Noise ( http://freespace.virgin.net/hugo.elias/models/m_perlin.htm ) as a possibility, but I my attempts have given me sporadic looking results. What are some techniques used to generate these 2D tile-based worlds?

Ideally I would like to be able to generate mountains, plains, and caves.