What are the best free or open source font editing/creation tools available for free on the Windows platform?
I've never designed a font, so I'll just say that Oleksandr's recommendation of Font Forge fits with what I've heard. Inkscape supports exporting laying out of images for export to Font Forge, so can be considered part of a font design toolchain.
Something nice about using free software font design tools is that they can make use of Raph Levien's Spiro-spline code, which is currently implemented in Font Forge and Inkscape; it is covered by a patent which can be used freely with GPL software and under license by non-copylefted software.
Spiro splines are really pleasant to use. Raph Levien wrote the algorithm towards his PhD thesis, wanting an algorithm that was better than cubic splines for his own font design.
My Font Tool for Tablet PC is a free tool provided by Microsoft in Microsoft PowerToys for Windows XP Tablet PC Edition.
I installed it once to try and it didn't leave me a permanent impression, but it's worth a try :)