On one of my machines, when attempting to build out a small SSIS solution none of the toolbox items were showing. Turns out there's a quick way to recreate/reset them.
Just delete the "toolbox*.*" files from the "%USERPROFILE%\Local Settings\Application Data\Microsoft\VisualStudio\8.0" directory.
Next time you open VS.NET 2005, it rebuilds from the defaults - you loose any customizations.
UPDATE: October 11, 2007 - you need to "see" these hidden files - I just did an "attrib -h tool*" in the directory, then killed with a "del tool*" from a command processor window.