Lets start this, but please add only apps you do USE yourself, so you can answer questions.
Also, please add the size the app needs on the USB stick!
So far, I use these on my USB stick:
name: Portable Firefox
size: ~18 MB
name: Miranda IM (ICQ, AIM, IRC etc.!)
size: ~1 to ~5 MB (depending on how much features and networks you want/need)
name: win32pad (Editor)
size: ~100 KB