'1284P is another option. 128K: 4x the Flash memory of ther '328P.
16K: 8x the SRAM (and twice that of the '2560).
Same great low power consumption in sleep mode with the 8-bit processor.
Easy to go SMD with - one of my very first PCB designs here in the forum:
1284P, FTDI, RS485, RS232, SD card, dual SPI UART for even more IO:
http://www.crossroadsfencing.com/BobuinoRev17/
for more examples