Portable Applications they just work and keep working.

When you computer hop as much as I do, not having to locate and install applications is nice.

Portable Applications are simply applications that run without being installed.

Your first point of call should be here.
http://portableapps.com/apps

Special Mention goes to
http://portableapps.com/apps/internet/filezilla_portable

and there are many more now, increasingly commercial vendors make them available as well.

UltraEdit and UltraCompare
http://www.ultraedit.com/products/mobility.html

A brilliant and lightweight colour picker.
http://nattyware.com/pixie.php

Real Time CSS Editor
http://css-editor.info/

HTTP File Server
http://www.rejetto.com/hfs/?f=dl