2Checkout allow annual billing, thoug they're a third party merchant solution.
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Do a search...there have been literally hundreds of threads on merchant accounts (and if you already have, my apologies).
I think allowing yearly payments would be predicated on the amount of time you have been in business and the amount of business you do per month. If you can prove to them that you are going to be around for a while, you might be able to work something out (esp. if you're going to make them a lot of money)