I think there is a decent market for a simpe, straightforward vending management solution.
This solution, in my opinion, needs to be mobile-friendly (perhaps a Google Docs template) or app-based (iPhone and Android app) so I can keep track of inventory and sales on the go.
A separate bank account with regular deposits seems to satisfy the finance tracking needs I have, but an inventory management solution that shows me (in a visually appealing, easy-to-understand way) what items sell best, what items are making you the most profit, etc. would be awesome.