Q: What is wrong with the firmware that came with my router?
A: Everything! The factory firmware usually provides a basic set of features through a kooky interface. DD-WRT will provide you with a rich feature set like those found on more expensive routers.
Q: Like what kind of features?
A: Dynamic DNS, Network monitoring, hotspot applications, security tools, firewall, web, ssh, & telnet interfaces and much much more!
Q: Which routers can I install this on?
A: DD-WRT supports many common routers that you can find at the store. Here's a complete list of supported devices.
I've had good luck picking up Buffalo Air Stations from Best Buy.
Q: Where can I download DD-WRT
A: From the downloads section of their website! Be careful to get the right release for your model router. Check the supported devices for more info.
Q: How do I install it?
A: This installation guide will walk you through all the necessary steps for your environment and hardware.
Q: Where can I learn more?
A: The DD-WRT Wiki is a good place to start looking for general info. The forum is very helpful for troubleshooting more complex problems.