Why am I not seeing all Payment Terms when adding a new customer?

When adding a new customer, the Payment Terms default to whatever default is specified under (Sales > Sales Setup > Customer Terms).  If you wish to assign a different Payment Term for the customer being added, you'll need to use the '...' button to launch a look-up for other terms.  The look-up, though, will be pre-populated with a search term equal to the default term.  So, you won't immediately see the other terms.  You first need to click the 'X' button that is beside the search field so that the search field is cleared.