1. What the Font!
Use this application to figure out the name of a font you want to use.
Since commercial fonts are often pretty expensive, use this site to find another font that looks close enough to make a good substitute for the real thing.
3. Are They Bootlegs
After you have a few names for the font you want to use, search this site (or scour google) for one of those names.
Tackorama has a lot of good fonts (as well as clipart and other images) divided up by specific eras.