If you have recently deleted a workspace from Eclipse and purged all the files from your file system, you may find it annoying that Eclipse will still show the workspace in the workspace launcher dialog. If you are trying to explain what workspace another developer needs to access, it can also lead to unnecessary confusion.

Ecplise stores the workspace history in a preferences file called org.eclipse.ui.ide.prefs located under %ECLIPSE_HOME%\configuration\.settings. The RECENT_WORKSPACES key contains a comma separated list of workspace paths. You can remove either the entire line (key & values) or just one value from the list.
Shutdown Eclipse, update the org.eclipse.ui.ide.prefs file and restart Eclipse and the workspace should no longer appear in the launcher.