Mostly this, but don't phone and don't phone again three months later. Might get a bit of attention, but many people hate needless interruptions like that. Send very brief emails, link to a portfolio (no Word or PDFs - link to your site). Don't send a bland Christmas card, but do send an email that's a bit more personal/casual. e,g, "Thanks for working with me this year. Hope you have some time off planned? I'm taking a break between x and y, but if you need a hand after that on any projects, please let me know. I've been working on a couple of interesting things recently (URLs) but I'm available in the new year."