I have been suggesting the RAMTRON FRAMs here for a while for external memory -
Benefits:
SRAM access speed, EEPROM data retention without 3.3mS write speed,
High Endurance 100 Trillion (1014) Read/Writes (vs mere 100K for EEPROM)
Ex: 3.3 or 5V 256K FRAM
http://www.mouser.com/ProductDetail/Ramtron/FM25W256-G/?qs=sGAEpiMZZMs6Aik9Fp479lX03Vi0JxwqYEefMzL7EC0%3D
Only drawback: Not available in DIPs