5-a-side TV. Given the ubiquity of football in general, there ought to be a market for some televised 5 a side. Would be seriously cheap to make, and I'd watch it. Probably.

Alternatively: a comparison website for price comparison websites. Now that you get meerkats/fuck-awful Brian robots etc when you buy through any of those berks, you need to make sure you're getting the best freebie deal. Needs a snappy title though, I don't have one yet.