FontCreator is a tool which can display existing fonts, let you modify individual characters to suit your needs, and design complete new fonts from scratch.
The program is equally at home with both TrueType and OpenType fonts (and can convert OpenType fonts to TrueType). And it supports all the popular encodings and code pages (ANSI, ASCII, Unicode, Symbol, Big5, PRC, Wansung, etc) so you can be sure that your creation will work wherever you need to use it.
Support for importing both vector files (EPS, AI, PDF etc) and bitmap images (BMP, GIF, PNG) helps get your design project off the ground quickly.
But there are plenty of other goodies which should appeal to more advanced users. So the program can fix character mappings, for instance, or edit and regenerate font names. It's able to generate, modify, import, export, and clean up kerning pairs. And with the ability to add up to 65,535 glyphs per font there are no real obstacles placed in the way of your creativity: you can do more or less anything you like.
Please note, FontCreator comes in Home ($79), Standard ($149) and Professional ($199) Editions. They're generally similar, but the Home Edition can't be used for commercial purposes, and is missing a few of the more advanced features (Automatic kerning wizard, "Insert characters" feature, font validation wizard, real-time glyph validation). See the full comparison here.
FontCreator has the advanced features experts need, yet is also easy enough to be used at a basic level by just about anyone.