I launched Open Exchange Rates (http://openexchangerates.org) - the Robin Hood of exchange rate (FX) data - which collects exchange rates every hour and distributes them for free via a GitHub repository, in a nice, clean, simple JSON API - with values going back to 1999.

It's currently running at 160,000 requests a day, from 45,000 unique IPs. Lots of those are mobile apps, lots of shopping carts, economics research projects - big users include Flattr, WooThemes (WooCommerce), and some other nice people.

Doesn't make any money because it was designed as a free service - but I'm currently re-architecting it from scratch to offer vastly improved features for a very small cost.

The data will always be free and open to anybody. The big fish I'm going for are partnerships with big institutions and colleges/universities, offering much more accurate and wide-ranging financial/economic data and statistics at a far cheaper rate than the current incumbents!