Diffing arbitrary deb-source packages

[Tom <tb.nospam@comcast.net>]

I've installed apt-listchanges and started reading the associated bug 
reports in changelogs when I upgrade unstable, so I'm doing a lot better 
understanding what's going on with my packages.

However, sometimes I find reading the source code helps me understand 
the developer's comments better.  Is there any easy way to "view a diff" 
of two versions of an arbitrary Debian source package?  My first choice 
would be online, ala CVSweb.  Ideally, I could read the changelog, bug 
reports, and code deltas side by side in an automated, general way, when 
I upgrade.

Thanks