Smaller version of the Mega I'm currently working on a Arduino Mega (GPS + IMU + SD card logging + BT). I need the Mega for extra memory and serial port. 
I would like to transition to something with a smaller form factor now. I need help with suggestions for a smaller form factor board/version of Mega.

Any suggestions?
I can't really find anything.

The only small size yet meeting requirements (in terms of memory) option seems to be a Microduino - 
but I'm not whether all the libraries (SDfat etc.) will work on this.
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.