From DD-WRT Wiki

Since there a many unbranded and unsupported Ralink based router out there, which have all similar/equal specs, there is a fair chance to get them running DD-WRT even if they are not officially supportey by this time.

[edit] Supported Hardware

There are a few basic specs that are mandatory for running DD-WRT on Ralink based router.

• >=4MB flash
• 32MB RAM (16MB RAM only on stripped DD-WRT versions)
• UBoot bootloader

[edit] DD-WRT Support

[edit] Flash Instructions

Install a serial connection to the device.
Check the supported devices list for units which use the same chipset and are already supported. Get some of the initial builds.
Install a tftp server.

[edit] RT2880F

This units have an external switch, so there is always a hardware donation needed for porting it to DD-WRT.

[edit] RT3050F/RT3052F

[edit] RT3350F

Flash the Buffalo WCR-GN initial build.