picking a FET for 12v use with Arduino
How much current do you require? 
For specs you want a FET with a breakdown voltage (BVDSS) above 12V and a current
rating that exceeds your load. A logic-level FET can sometimes be better but it
probably will not matter if your current requirement is only a few amps.
N-channel is usually what you want.

I use the On-Semi NTP65N02 with a 3.3V gate drive level for a current-sink.
TO-220 package and a fairly low Rds(on) at that level.