If you are running FireFox (or Chrome) then there is a handy little short cut you can use to view the source of a page you are looking at. If you add the text view-source on any web address then you will see the equivalent of viewing the source of a page (perhaps by pressing Ctrl+u). Although not entirely useful, it does have a couple of benefits, such as being able to view your code in another tab, rather than another window.
Unfortunately, this only works in FireFox up to the latest version (currently 3). I have tested this in IE 7, Opera and Safari and they all complain about invalid protocols. Apparently it used to work in IE 6 before SP2, but was removed with that patch. This leads me to believe that it is not really a protocol, but a command that the browser understands on a local level. Much in the same way as about:config works.