The TrueType font format is used by Windows, Windows 95, and Mac's. It is quite popular and there are a great number of fonts available in this format.
Unfortunately, there are few applications that I am aware of that can use this format: Ghostscript and Povray come to mind. Ghostscript's support, according to the documentation, is rudimentary and the results are likely to be inferior to type 1 fonts. Povray version 3 also has the ability to use TrueType fonts, but I rather doubt many people will be creating documents as a series of raytraced pages :-).
This rather dismal situation may soon change. The FreeType Project is currently developing a useful set of FreeType tools:
The xfsft font server for X11 can serve TrueType fonts in addition to regular fonts. Though currently in beta, it is said to be quite usable. See Juliusz Chroboczek's page for further information. Porting instructions for FreeBSD can be found at Stephen Montgomery's software page.
xfstt is another font server for X11, available under ftp://sunsite.unc.edu/pub/Linux/X11/fonts/.
A program called ttf2bdf can produce BDF files suitable for use in an X environment from TrueType files. Linux binaries are said to be available from ftp://crl.nmsu.edu/CLR/multiling/General/.
and others …