Just an FYI, if by clients you mean for consulting work, Freshbooks has an arrangement w/ Paypal (yeah, I know) where payments are a flat $.50 (yes, 50 cents) for all invoices up to $10,000. You will still have to put up with a wait to get that money in your bank account (3-4 business days if payment is immediate), but it can all be handled online. I've had all my payments over the past year go thru Freshbooks and the lifecycle of invoices/payments is tracked in their system.