It was hard to find this as I find most online payment processors don't just put the basic information in plain view.
Remember to set your sid (your seller id). The below can easily be turned into a scripted PHP template to integrate into your own custom or existing payment solution.
http://help.2checkout.com/articles/How_to/How-to-Sell-Recurring-Products-with-2Checkout/
<form action="https://www.2checkout.com/2co/buyer/purchase" method="POST">
<input type="hidden" name="sid" value="XXXXXXX">
<input type="hidden" name="mode" value="2CO">
<input type="hidden" name="li_1_price" value="10.00">
<input type="hidden" name="li_1_name" value="This is my Product">
<input type="hidden" name="li_1_tangible" value="N">
<input type="hidden" name="li_1_quanity" value="1">
<input type="hidden" name="li_1_startup_fee" value="-2.00">
<input type="hidden" name="li_1_type" value="product">
<input type="hidden" name="li_1_recurrence" value="2 Week">
<input type="hidden" name="li_1_duration" value="1 Year">
<input type="submit" class="submit" name="purchase" value="Buy from 2CO" />
</form>
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