Well, your mileage may vary. But here's Multifolaterose's report on self-esteem before:

Though I hate myself for it, apparently I care a lot more about myself than I care about other people. I’m just not a good enough person to do what I should do. I’m happier when I don’t think about it than when I do, and I do the wrong thing regardless, so I try not to think about it too much. But I know in my heart-of-hearts that the way I’m leading my life is very wrong.

and after:

What effect did donating have on me? Well, since correlation is not causation, one can't be totally sure. But my subjective impression is that it substantially increased my confidence in my ability to act in accordance with my values, which had a runaway effect resulting in me behaving in progressively greater accord with my values; raising my life satisfaction considerably. The vague sense of guilt that I once felt has vanished. The chronic mild depression that I'd experienced for most of my life is gone. I feel like a complete and well integrated human being. I'm happier than I've been in eight years. I could not have done better for myself by spending the $1500 in any other way.

To see why multifolaterose thinks it might happen to you, read the article, especially reason (C) for why happiness correlates only weakly with disposable income and the quotes from Singer's book.

Hope that helps.

Also, at the risk of being preachy or presumptuous, Multifolaterose doesn't predict that you'll get any significant character gains from throwing a few bucks around here and there -- you would have to give in an amount that begins to reflect your values. Spending 1% of your income on charity, e.g., suggests that you value yourself 100 times more than a stranger, which may not do much for your self-esteem.