I discovered an option "View -> Toolbars -> Compiler". However it doesn't seem to be doing anything.
This is the correct toolbar, normally containing a set of five buttons relating to the build process and the Build target dropdown.
If it's become totally lost somehow, you might try resetting Code::Blocks' configuration to see if you can get it to reappear. Find your Code::Blocks config file, usually named "default.conf" and residing in "Application Data\codeblocks" in your user directory, and rename it to something else to force C::B to create a new one.
If this works, you can then reapply all your preferences by hand in C::B, or try restoring the old config file and editing/deleting the layout section.
If it doesn't work, there's a bug somewhere in C::B or wxWidgets -- and the odds are that it's Vista-related.