Digital Insanity has now added a Feed The Beast server for advanced Minecraft game play. This is a heavily modded, highly technical version of Minecraft with hundreds of new items and crafting recipes. Play can include things such as solar panels feeding battery banks that will power pumps that will transport items from a process unit that converts wood into coal into a chest for storage. It can get pretty wild the amount of automation that can be put together. Download the client and give it a try at http://feed-the-beast.com/
Members go here to get the server information.