0irc is the smallest known (IRC) Internet Relay Chat client in the world for windows. Not only does it have a small footprint, but also contains a small set of necessary features.
X-Blender is based on Blender (Popular Open Source 3D Creation Software) but contains a wrapper to allow a user to run it directly from a USB drive. With this portable 3D tool, you can model, shade, render and create all kinds of 3D graphics and effects.
Portable Scribus is a stand alone, USB flash drive installable version of Scribus, the very popular open source free desktop publishing tool. This portable application makes for a great alternative to Adobe PageMaker and can be used to create professional looking documents, PDF files, newsletters, magazines and much more.
TTCalc Portable is a nice advanced Mathematical calculator. Available in both English and Polish languages TTCalc is so simple to navigate and very easy to use.
KeePass Password Safe is yet another great Portable Password Manager that can be run directly from a portable USB device. This application allows you to put all of your passwords in one database, which is then locked with a single password or master key disk.