Mosfet: dual n channel 20amp IPG20N
http://www.mouser.com/Semiconductors/Tr ... 0N&FS=True

There are many choices, I narrowed it down to this one as it has low on-resistance and is fully on at 4v gate (3.3v it will peek to 30A)
http://www.mouser.com/ProductDetail/Inf ... h8nw%3d%3d

The SMT heatsink is this one:
http://www.mouser.com/ProductDetail/Wak ... 89NQ%3d%3d
The pattern does not have pads, it just leave a solder mask opening.

This is what you can do with them:
viewtopic.php?p=5011#p5011
notice that I run gate-trace on bottom to max ground plane on top layer to help with cooling.