DD-WRT is a really nifty open source project for turning your boring old wireless router into a modern, full featured router. From the DD-WRT web page:
DD-WRT is a Linux based alternative OpenSource firmware suitable for a great variety of WLAN routers and embedded systems. The main emphasis lies on providing the easiest possible handling while at the same time supporting a great number of functionalities within the framework of the respective hardware platform used.
Setup is pretty complicated, though. Here is how I did mine.