Add a “Gmail this” bookmarklet to your web browser

javascript:(function()%7Bm='http://mail.google.com/mail/?view=cm&fs=1&tf=1&to=&su='+encodeURIComponent(document.title)+'&body='+encodeURIComponent(document.location);w=window.open(m,'addwindow','status=no,toolbar=no,width=575,height=545,resizable=yes');setTimeout(function()%7Bw.focus();%7D,%20250);%7D)();

This browser bookmarklet, “Gmail This“, creates a new Gmail message containing the URL of the web page you are viewing.
Just drag it to your Bookmarks Bar (Safari/Camino) or Command-click on it and select “Bookmark this link…” (Firefox).
That’s it.