Hi,
Love this site, so I thought i'd (attempt) to contribute. 2 programs i'm currently running off USB that seem to work fine but aren't listed here as far as my searches go -
Auslogics Disk Defrag, freeware. Has installer, but once copied all files apart from uninstall files to USB folder have been able to successfully defrag HDD without install present (on other PC's). Has a nice interface, and is very fast. http://www.auslogics.com/disk-defrag/
DP CD DVD Burner, freeware. Comes in a zip file, does rely on wnaspi32.dll for burning, however, within the "new_aspi" folder in the zip it contains the dll for you, simply copy to where main executable is. So far works fine in regards to portability, however not sure if anything is written to HDD, or left behind. http://www.freewarefiles.com/program_6_205_23365.html (linked to freewarefiles.com as their site isn't very easy to navigate) Plugins available here: http://www.paehl.de/dpburn/ or click on plugins button within program.
Hope these are OK