A lot of folks are pleasantly surprised when they get a message saying, "Hey, I don't need anything. I'm just dropping you a line to..." I've found this works really well during holiday seasons or if you know something personal about them like a birthday. Much better than e-cards.

If they don't bring it up proactively, your next contact about a job will probably be very well-received. Personally, I would always try to check-in with someone, once, months before you asking them for something.