Mia,

Brent Ozar addresses some of this (http://www.brentozar.com/archive/2009/03/are-you-being-treated-fairly/) in his blog post.

If a manager doesn't appreciate what you've done, re-examine it and be sure that you have gone above and beyond. Talk to someone else you trust and see if you have really done more than others.

If you have, I'd look for a new position. The best time to get another job is when you don't need one.