I looked all over the internets for this little gem…
In default.master, add ItemWrap=”True” inside the <SharePoint:AspMenu> tag that has an ID of “TopNavigationMenu”.
Like this:

Mucho thanks-o to The Mossman for answering a post in the MSDN forums.
Tags: long site title, long title, SharePoint, top links bar, top nav bar, top naviation bar, word wrap, wrap text