GlyphTool is a standalone app, and API (including some example programs and code) for quickly and easily integrating full color text into OpenGL for games (or anything you can think of).

The main program (in screenshot) is used to generate a texture with characters on it that will be split up by the API and used to render text in game by the glyphtool API.

The API comes in two flavours, C (useable with C++ and for making bindings to other languages), or Objective-C (using plists and object oriented structure for the fonts).