What should marketing contractors get paid per hour?

I have been doing marketing contract work (press releases, viral video production, event organizing, consulting, graphic design, web content, etc.) for a friend and am working for almost nothing ($25/hr). At the same time, I have a contract for similar work with a big software company and they pay me twice the amount my friend pays me ($50/hr). Until 6 months ago, I had been working in non-profit sector, so my perspective on normal pay rates are skewed. I wanted to get some ideas from folks out there as to a standard rate for marketing contract work.