Your best option would be to use either Payflow Pro or Website Payments Pro and use reference transactions with each of those. The both would allow yout o process credit card transactions dierctly, and you could add recurring payments/recurring billig on as well if you wanted to set up a profile for the customer to be billed.
One problem that you would have if you use Express Checkout and you set up recurring payments, you can only increase the amount by a certain percentage. If you use reference transactoins you can process additional transactions without having to ask the customer for their billing details again.
Even if you didn't want to use the recurring billing/recurring payment system through PayPal, you could just use reference transactionis and set your system up to bill the buyers on a recurring basis using rference transactions.