erewards is great to keep accounts of infrequent travelers active. You can earn survey dollars quite easily and then convert them into a number of different programs. I think miles would be delta, us air, alaska, continental and flying blue. Hotels are limited to hilton best I recall.
You can earn $100 survey dollars with minimal effort over the course of a year and then break up redemption into $25 increments to keep four of your programs alive at no cost to you.