I have been working at my current job for almost 5 months. When I was hired, I was given a salary figure but promised a raise after 90 employment. Basically the first 90 days were probationary and the intial hourly pay was a " low ball" figure. After 90 days my pay has not increased. How do I bring it up that I have not received my raise? I know my market value and I am currently receiving almost 4 dollars less per hour than other places. Any advice on how to bring this up?

Did you get an employee handbook? Sometimes the process for asking for a raise is outlined there. Otherwise, I'd ask my supervisor for a meeting to suggest a pay raise, so that he or she can have time to think about it before you ask him or her.
What's your workplace like?