I just put together a standalone 2560. Its 1.6 x 2.6’’, and weighs in at 12 grams. It has the FTDI chip and a micro usb connector. It has an external crystal, and a 5v regulator onboard. I’m going to do a Kickstarters project within the next month to try to get the cost down. I have some working now, but the final ones should be ready in another month. I just have not got around to posting all the info on it yet.
The board has double rows of pins on three sides. I was working on making something that was a bit more embedable in my projects.
Let me know if your interested. I have an extra rev1 board and can send a BOM. Parts were $37.00 not including the board