IMHO, the only real taste of big money I've had during the last couple of years is by selling IM services to HUGE companies. Fortune 500 companies need backlinks, video views and facebook likes just as much as anyone else.
Before you go out selling this to those guys, remember these points:
1. You need someone that has access to decision makers at these companies, so there must be a legit looking PR
company or ad agency in the middle.
2. Do not tell the big co. the details about what you do for them.
3. You need metrics. If the low level managers at the big co. can not see results in the stats, they can not convince the middle level managers to put more money into this.
4. Decision makers at huge companies do not understand IT. They can barely switch on a computer. So dumb it down.