The TP-Link WDR4300 (v1.6) has an impressive array of hardware features and 128M of RAM for about $160. Unfortunately it comes with firmware that the vendor has deliberately crippled and a known backdoor.
Fortunately the amazing OpenWRT exists so we can make this nifty little machine work really hard for us doing a wide array of things. Here's how you get OpenWRT onto this router:
Check the model version underneath the router (You really want v1.6 - the others work but this is the best one)