TP-Link WR703N is a OpenWRT supported Wi-Fi router that comes with ‘only’ 4MB of flash and 32MB of RAM. If you are not satisfied with these, they are easily upgradable as described in the forum.
RAM can be upgraded to 64MB if you are not afraid of hot air soldering. Just take out one chip from a 512MB DDR 333MHz SODIMM module and replace the one on-board…
It looks like you can replace the 4MB SPI Flash by an 8MB (MX25L6445EM2I-10G SOP8), but this would require an SPI Flash programmer (BusPirate?) to backup and restore the Flash.
Check out more information on the 64MB RAM mod on the openWRT wiki. Also available is a GPIO hack that gives you access to a software I2C port (pictured above).
Via the forum.