Would it be possible for PA to have a specific forum or a dedicated page (with a link at the top) with a listing of other applications (still "safe" and recommended, but possibly closed source) portable applications?
I think it might limit the number of requests seen in the apps request forum, and also inform visitors that there are applications already portable out there---PA just can't host them here since they can't be made PA portable. PA doesn't need to host the software; it would just need a link to the homepage or portable build page, and include a short discussion on how to make it portable.
I am sure that an official list of tips and tricks wouldn't take long to create with this community.
Some recommended bits of freeware (free as in free beer) that immediately come to mind...
CCleaner, Recuva, and Defraggler are file/system management tools from Piriform--all have portable builds.
CCleaner - http://www.ccleaner.com/ - http://www.ccleaner.com/download/builds
Recuva - http://www.recuva.com/ - http://www.recuva.com/download/builds
Defraggler - http://www.recuva.com/download/builds - http://www.defraggler.com/download/builds
Foobar2000 is an advanced audio player and media tool that has a portable installation mode.
Foobar2000 - http://www.foobar2000.org/
TrueCrypt is an advanced file/drive encryption tool with a portable extraction in the installer. It does require Administrative rights to operate.
TrueCrypt - http://www.truecrypt.org/
CDex is an advanced CD Ripper, but I am not sure if it is portable (there is an extractable ZIP archive of the program).
CDex - http://cdexos.sourceforge.net/ - http://cdexos.sourceforge.net/?q=download
Peerguardian Lite is a CL version of the popular PeerGuardian. It is Open source too.
Peerguardian Lite - http://phoenixlabs.org/pglite/