TagScanner is a multifunction program for organizing and managing your music collection. It can edit tags of most audio formats, rename files based on the tag information, generate tag information from filenames, and perform any transformations of the text from tags and filenames. Also you may get album info via online databases like freedb or Amazon. Supports ID3v1, ID3v2, Vorbis comments, APEv2, WindowsMedia and MP4(iTunes) tags. Powerful TAG editor with batch functions and special features. Playlist maker with ability to export playlists to HTML or Excel. Built-in player.

Toucan allows you to synchronise, backup and secure your data. It features four synchronisation modes: copy, update, mirror and equalise. It creates backups using ZIP or 7-Zip formats. Encryption is based on the Blowfish algorithm.

Notepad2 is a small and fast text editor with syntax highlighting for HTML and other common languages. It supports modeless find and replace dialogs, multi-line find and replace operations (using backslash expressions), optional file change notification etc.

The GIMP (GNU Image Manipulation Program) is an image editor for photo retouching, image composition and image authoring. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter etc. GIMP Portable is a portable package for the GIMP, so you can take your images with you and do your editing on the go.

ClamWin Free Antivirus is a scanner for viruses and spyware. The virus/spyware database is constantly maintained by a group of volunteers, and you can always get the latest updates via the Internet. Note that ClamWin Free Antivirus does not include an on-access real-time scanner i.e. you need to manually scan a file in order to detect a virus or spyware.

ClamWin Portable is a portable wrapper for ClamWin. You may also want to check out ClamWinPortableDBUpdate that automatically updates the virus definitions database in your ClamWin Portable installation periodically or during startup.

Opera is a fast and secure web browser that features pop-up blocking, tabbed browsing, integrated searches, built-in email and RSS client etc. OperaUSB is a portable package for Opera that does not write to the registry nor leave any data on the guest machine where it is run.

Another alternative is Opera Portable. Thanks to TheReaper for suggesting this.

BFilter is a filtering web proxy. It was originally intended for removing banner ads only, but since then its capabilities have been greatly extended. It detects web ads heuristically (like modern anti-virus software) as opposed to using blacklists, which results in much more consistent behavior. Note: Configuring a portable browser to use BFilter works flawlessly as long as BFilter is running, though it is not recommended to do this with a browser on the host computer. Configuration instructions can be found here.

Encopy rescues data from damaged media when standard system copy fails, freezes and or rejects the media. In cases where it is not possible to perform a full recovery, Encopy will try to copy as much data as possible from the damaged files.

AoA Audio Extractor allows you to extract audio/sound or background music from video files. It supports extraction from AVI, MPEG, MPG, FLV (Flash Video), DAT, WMV, MOV, MP4, 3GP video files and exporting the audio as MP3, WAV and AC3 audio files. It can also be used to save any portion of the audio of a video file.

XMedia Recode is an audio/video converter. It converts most audio/video formats such as 3GP, DVD, AVI, MP4, WMV, ASF, etc. so that they can be played on popular mobiles devices/PDA such as iPod, iPhone, Samsung, SonyEricsson, Zune, PSP, Blackberry, LG, etc.

Note that the website is in German, but the application supports English.