I asked for, and got, a raise about a month and a half ago. In the summer I was inadvertantly handed my co-worker's pay stub by mistake. Not realizing that it wasn't MY pay stub, I opened it and peeked inside. When I saw the increase, I assumed I had been given a raise due to the recent work load increase that I "inherited" when our manager quit. But when I opened the envelope and removed the entire pay stub, I saw that it wasn't MINE.
Anyway, long story short, I went to HR and told them (for many, many reasons) that I felt that I deserved a "salary adjustment", due to my new increased work load, and due to the 35% difference in salary between myself and my co-worker. I told them the truth about why I wanted the increase; that if they felt that she deserved her salary, then I feel that I deserve a bit more (but still less than her) than I was currently making.
The owners agreed, and I ended up with a 20% increase.

She's worked for the company for about 9 years longer than I have, so I feel that her 15% more is fair.
It may have been an unconventional way to ask for a raise, but I trusted my own instincts, wasn't afraid to ask, and ended up with the raise that I wanted.
I think you should ask for a raise if you feel that you deserve one!