I've only tried Glyphr[0] because it's online and gbdfed because it was in my linux distro's package manager and it was small (turns out it was a bitmap editor, which was fun to try out, but now I have a .bdf file that I don't know how to use). I can't really recommend these because they are the only ones I've tried, but Glyphr is simple though it doesn't have that many features.

Then find a way to use the font, like on a website, and you'll notice any problems or ugly parts.

[0]: http://www.glyphrstudio.com/