If you have the skills/knowledge to find bugs that would be your most profitable venture chances are.   If you can find security concerns and turn them over to the company a lot will pay nicely.  Heck i think the forum here even does a bug program.

I would suggest raising rank and joining a signature campaign.  It's a nice little extra for doing something you would do anyways.   Higher your rank better it is.

Selling goods/services might be your best bet though.