Why do I want to run DD-WRT firmware on my router?

Solution 1:

Others have mentioned the main features, so here are some of the more esoteric ones:

Run multiple SSIDs, each with their own routing and firewall rules.
SSH server built in. You can log into your router from the Internet, then log in to your home machines.
Speaking of SSH, it supports port forwarding.
Split the LAN ports on the back and the wireless LAN into (up to) five distinct LANs, each with their own subnets, DHCPd, routing, and firewall rules.
On some models, boost the power output of the wireless radio up to the legal maximum (250 mW).
Run a public hotspot using the built-in Chillispot, Sputnik, and Wifidog software. Optionally display ads to hotspot users.
RADIUS authentication.
QoS bandwidth limiting, configurable on a per-protocol basis. Some versions of dd-wrt include gaming accelerators.
True VLANs, with tagging.
Ethernet-over-IP tunneling.
Wake-on-LAN. It automatically maintains a database of MAC addresses it knows about. Click a button to wake up that machine.
Built-in lookup of MAC address manufacturers. Just click on any MAC address you see in the GUI and it'll show you who made that network card.

There's more...much more. I buy and recommend routers based on whether I can install dd-wrt on them.

You can setup the router to be a wireless bridge.