I missed something on MyFont the first time: their WhatTheFont?! service. You upload an image of some text, help the software pick out individual letters, and then some magic happens and it comes up with a list of matching fonts.
Pretty useful but not exact. For instance it can't quite match the Google logo font. The closest match Diaconia is handsome but not quite right - the Google logo font has an odd lowercase 'g' with the connector on the right, not the left. Serifs are off too. Still, WhatTheFont?! is useful for the "find me fonts that look like this" problem.
MyFonts credits the University of Birmingham for development of WhatTheFont?!. They also point to Identifont as another font finding tool. Identifont looks like an expert system: answer a bunch of questions and it comes up with candidates.