We're really big on yearly client anniversaries here and have sent everything from
gourmet chocolate bon bons to a
printer/fax/scanner/copier with reams of recycled paper

.
Our gifts (the cost of) at the one year mark are usually based on a few criteria - how much work the client has sent (ie - total invoices) AND equally important to consider, how many referrals we've contracted as a result of their kind and positive word of mouth on our behalf. We have one client that we joke with about sending a car at some point. And I suppose, as we continue to grow there really will come a point when that happens, LOL.
We've also sent flowers, marketing/small business books that we thought the client would find useful, discounts are a good and more basic gift, we've gifted an entire invoice as on-the-house as well.
Hope that helps! And congrats on a year in business with a good client!!