Randy,
The best system I have seen is the amercian express business card, they require the purchase information to reflect the description of the purchase, they really track things and will call you if even the appearance of wrong doing comes up, easy to use and the repores are great saves you a lot of paper work they even sort some billing by class or tax , something to look at before you go into a purchase order system, many of the fortune 500's are goint to the corporate credit cards, and what is really nice you can issue different cards to the employees that are using them with custom limits or special job or project tracking
