Bento For Business is a prepaid debit card that you can load online. I'll keep a balance of $500-$1000 on it, and after the manager makes a purchase will scan in the receipt. After reviewing the receipts I'll top up the card. You can also limit what types of stores purchases can be made at.
Chase also has a business credit card called Ink I'm trying out where you can get additional cards with low caps on the balance.