Help! I accidentally deleted "Button" from my Widgets in the Toolbox

I accidentally deleted the "Button" widget from my toolbox in the IDE, and now I can't find it to restore it.  Can someone please walk me through this?

I know- really a dumb question... but it's really frustrating when trying to learn a new IDE you have to stop everything to correct a seemingly simple mistake.

I am running Mono Develop in Ubuntu Hardy Heron.

Thanks in advance for any help.

-Chris