Opera
One of the fastest web-browsers for Windows out there. Many configurable items, and you don't need to slow down your startup time with plugins because all the features all ready come with Opera. Not to mention it has even less of a user-base than FF, hence more 'secure'.
CCleaner
Like Cleanup! but has a registry cleaner.
Pidgin
Better than Trillian.
Foobar2000
Winamp stopped being good around 3.1. Foobar2000 is excellent for that "background music" you need when you're working on homework or playing a computer game. This is because the default GUI is extremely simple. Foobar2000 is intended to not function through the GUI, but through the hotkeys in which you program into it.