Just a word of caution. If you are issuing corporate cards then you need to have a section of your travel policy (or better yet a separate policy) that talks about the dos and don'ts with the corporate credit cards. Spending limits, approved expenditures, process to get exceptions pre-approved, where and when to turn in receipts, what the consequences are if someone is caught using the card for personal use, etc.
I would do a google search on corporate credit card policies and see what comes up. You are probably going to find a lot of state agencies, universities and college policies, but that may get you started on things to consider.