* Running a bitcoin mining pool and accepting donations/small transaction fee
* Running an actual bitcoin bank
* Creating a meetup type app for bitcoin traders, would be very useful for Canadians and other non-US citizens where purchasing bitcoins is difficult
* ForEx software for bitcoins. The fluctuations in price seem to be as random as real currency anyway, ForEx software and training is a very profitable industry.
* Renting out or building bitcoin PC rigs with the latest GPU processing power
* Bitcoin analytics, providing latest stats on potential bitcoin mining profit margins given the cost of electricity, video card hardware costs, and current trading price.
Apart from that, as the bitcoin economy is still in its very early stages, everything that looks more professional and trustworthy than a cobbled-together PHP script on a dirt-slow server could become a huge success.