I have a project where I would like an extra serial line and some more memory, like what we get on a Atmega644P. What are the current options for an inexpensive Arduino-compatible 644P board?
http://www.crossroadsfencing.com/BobuinoRev17/
$5, supports 324/644/1284 family.
PL & schematics.
onboard USB/Serial with MIKROE483 from mouser.com, or offboard with your choice of USB/Serial adapter.
You have also the Wiring Project :
They have a board with a 644