Fony
Fony is a bitmap font editor developed by hukka and released for Windows in 2008 using an unobtrusive nagware model. It supports several old bitmap font formats. It can open, modify, and save Microsoft bitmaps fonts (FON, FNT), Amiga bitmap fonts, Bitmap Distribution Fonts (BDF), and Bitmap Font Writer fonts. It can import an image into a bitmap font and export a font into a bitmap sheet. It can also convert a True Type Font (TTF) into a bitmap font.
The program hasn't been updated in a while, but the latest version is a pretty great bitmap font editor.
Download
This is the last stable version.