Here are a couple of excellent websites which post a LOT of content about Arduino/ATtiny related topics.
This is a blog run by someone who has invented their own platform similar to Arduino but called a JeeNode. The main difference is that a JeeNode includes an RF link. This is actually pretty cool as a complete JeeNode is only EUR18.50!
This site is frequently updated with interesting hacks which people have built around ATtinys.