bondsonline, a competitor to bondtalk (a recent site) has news, quotes, and information on Treasury bonds, Munis, Corporate bonds, and savings bonds, as well as discussion forums.
(suggested by Kendall Miller) Bondtalk has bond quotes, news, FOMC (Fed Open Market Committee) schedule, definitions, and more. For example, you can read here the surprisingly vague definitions of bond ratings.
The Emerging markets Companion has a wealth of information about international debt markets, including current prices and analysis as well as background information. For example, have a look at the Brady Bond Primer for an introduction to Brady bonds.