Great advice from Seth, at Your brand is not your logo:
Smart marketers understand that a new logo can't possibly increase your market share, and they know that an expensive logo doesn't defeat a cheap logo. ... take the time and money and effort you'd put into an expensive logo and put them into creating a product and experience and story that people remember instead.
Amen! You can spend a lot on creating a logo, or you can get your nephew to do it on the cheap. Either way, what you end up with isn't all that important.
What you do is what matters. Does it excite donors? Does it make them tell their friends? Do they talk about it on their blogs or MySpace pages? Figure that out, and you won't have to worry about your logo.