Smaller version of the Mega
The ATmega1284P provides 128kB of flash, 16kB of SRAM, 4kB of EEPROM, and 2 USARTs in a 40/44/49-pin package. Mighty 1284P provides Arduino support for the '1284P.

There aren't too many actual boards that feature it, but it can be used very easily on a breadboard or custom PCB with a programmer.