I would love an app that would allow me to dynamically generate business credit cards for use with paying stuff online. Whenever one of my 20+ recurring payments get compromised, I then have to spend half a day going through all my recurring payments providers and re-issuing with a new card. I would much rather have one card for each one.

There was a startup working on this but unfortunately they closed down before they launched. I still think this is a really interesting idea and someone should implement it. I suppose you could just use the Stripe API for most of the heavy lifting. I would actually start this company, I think it's that good of an idea, but unfortunately I'm little busy at the moment.