I recently came across a site (Open Source God) which provides a "round up" of Open Source applications.
I think it's a useful source of information.
http://mashable.com/2007/09/23/open-source/
If you read the comments on the site, you will find different opinions and two other similar sites are mentioned ...
http://www.osalt.com//
and
http://www.digitaldarknet.net/thelist/index.php
Note that Open Source apps are of course not necessarily portable; but several are!
I hope this is useful for some.