I'm not a techie like you guys, and I seem to be driving in the opposite direction --- I'm trying to minimize my software to the essentials. If I find a multi-function app that does 90% of what several standalones combined can accomplish, I tend to ditch the standalones and keep the multi-function, unless it lacks an essential operation.
Watch out, I'm in babble-mode today! More than you ever wanted to know about my drive ......
I have about 500 mb of frequently-used apps, and 320 of that is two apps! (OpenOffice and Audio Cleaning Lab)
LAUNCHERS
Qsel 200 KB (plus my home-made custom icon sets)
Launchy 3 mb
Launch/search from keyboard instead of mouse.
Toolbox 2.2 mb (plus cached icons and background images)
Extravagance! To raise the cool factor, I configured a toolbox with a full-screen background and links to be a take-along desktop.
FILE MANAGEMENT
FreeCommander 2 mb (kill unused lang files)
Tabbed dual-pane file manager with integrated file viewer, zip/sfx tools, useful screenshot utility, secure delete; sync folders; much more. Arranging columns is a pain, though.
Universal Extracter 6.5 mb (upx'd). Unpack archives & installers.
Lupo's UpxTool+ 0.3 mb. Compress binaries. Easy drag&drop interface.
The Font Thing 0.5 mb (JauntePE)
Fonts manager, load "uninstalled" fonts to work with open apps.
FileSeeker 1.7 mb (UPX'd from 5.8 mb)
Super-fast search tool. Boo -- large DPI display sends Stop button out of sight. Can't find any documentation.
SECURITY
BlowFish Advanced CS. 0.5 mb (kill unused lang files)
File encryption; secure deletion; launch associated app to edit encrypted docs, then "auto" re-encrypt when done. (Watch out, some apps "auto-save" don't self-clean unencrypted temp copies.)
KeePass 1.2 mb -- password manager
ClamWin 17 mb -- antivirus scanner
UTILITIES
IE Privacy Keeper 0.3 mb (UPX'd) cleans surfing tracks.
cCleaner 0.3 mb (UPX, killed unused lang files & unicows.dll)
TPFC page says admin rights required, but I've used it for file and registry cleanups without them.
Defraggler 0.3 mb (upx'd) -- defragment drives or selected files
UndeletePlus 0.6 mb deleted files recovery
Cobian Backup 6.5 mb (UPX)
GADGETS & GIZMOS
CAFE Mod 0.2 mb
File associations without registry entries. Sadly, only seems to work on Windows Explorer, not with any alternative file managers or launcher I've tried.
Convey 0.6 mb
Portable custom "send-to" targets on explorer right-click context menu without registry entries. Does work with the alternative file managers I've tested.
DM2 0.5 mb
a variety of useful windows shell enhancements
Portable TaskBar Shuffle 500 KB
Re-arrange taskbar buttons and systray icons
WinXmove 0.5 mb
Eases moving and resizing windows (good if you have problems snagging borders)
TitleBarClock 35 KB (JauntePE)
Puts time & date on active window caption bar

.
BUT, uses 6 mb memory
OFFICE TOOLS
OpenOffice 170 mb
So far I only use Writer (exports to pdf beautifully, even keeps hyperlinks!) { someday, if ever Calc supports Excel VBA macros......}
CryptEdit 1.8 mb including RichEdit and SpellCheck dlls (wrapped with JauntePE).
Tabbed rich-text editor; Old and utilitarian and all I need most of the time. Supports OLE object insertion; email integration; live URLs; low-grade RC4 & MD5 encryption of files on disk.
No header/footer support. Import / Export of Word, Word Perfect, Write, Excel docs requires installation of MS converter pack version 1.2 to C:\Program Files\Common Files.
Jarte 5.4 mb (UPX)
Rich-text editor can save to Word format. Good feature-set and non-standard interface is quite pretty, and icons & labels are just too tiny for me to use comfortably; I'm trying to memorize the interface. "Minimal" view is VERY minimal. No compiled help file included in v 3.0.
kPad 100 KB (JauntePE, UPX)
Tabbed rich-text editor, so small it is my notepad replacement. From the famous Floppy Office.
KeyNote 2 mb.
Tabbed tree-style app for notes/PIM/simple rich-text editor. Houses all my passing thoughts and screen-grabs and weblinks and nonsense.
BlockNote 1.6 mb. (JauntePE, UPX)
WYSIWYG web editor -- as easy to use as a simple word-processor, no html knowledge required.
PDFx-change 3 mb (JauntePE, UPX, delete help files)
PDF viewer supports mark-up and pdf layers.
*Still* waiting for "copy formatted text".
TheSage 21 mb dictionary (better for definitions)
WordWeb 9 mb thesaurus (better for synonyms)
TabbyCalc 0.7 mb.
Calculator keeps running log of your data entries & notes.
I like the old version 1.2 interface better.
Convert 113 KB (UPX)
Weights & measures unit converter.
MEDIA
1by1 Audio player 160 kb naked, size increases with WinAmp dll plugins to enable playback of various formats.
VLC media player 10 mb. Carries its own codec pack, plays almost everything.
Audacity 2.8 mb (killed 2 mb lang files, added 1 mb of upx'd VST filters)
My audio editor for 5 years, even before it was portable
Magix Audio Cleaning Lab *payware* 150 mb (JauntePE, UPX)
Software dedicated to noise removal and audio enhancement. Also rips and burns. Well worth the $30.
BeLight 2.7 mb (JauntePE, UPX, wipe unused lang & readmes)
Audio format converter. Supports Wav, AAC, AC3, MP2, MP3, Ogg, FLAC, and can extract soundtracks from avi and dvd VOB files (but not DTS). Easy-to-use presets, or configure it your way.
ImgBurn 1.8 mb
I've used it since its birth to burn video dvds, and now v 2.4 can make audio cds too. No coasters.
IrfanView 9 mb (SmithTech's PAF version)
Image viewer (also plays many media files) and simple image editing.
PaintBox 0.5 mb (JauntePE to trap a few registry writes, UPX, deleted help files)
Entry-level graphics editor, midway between MS Paint and PaintDotNet. I use it for small quicky projects (Paint Shop Pro on my hard-drive otherwise)
Pixie 7 KB
Color picker displays RGB, hex, html values. Hot keys for many extra features.
IcoFX 1 mb (UPX, kill unused lang files)
Very nice Icon editor. I use Microangelo for primary icon creation, IcoFX to create custom 16-color palettes and add effects --- but new v1.6 has improved the Zoom, so I might retire Mike. (grrrr -- compiled help file has been dropped in favor of online help.)
Video editing - I don't carry any portables, my projects are too large. But I recommend DGI for demuxing Mpeg/Vob files, VirtualDub & VirtualDubMod for editing, HCenc or QuEnc to encode avi to dvd-compliant m2v, DvdAuthorGui to author m2v & mpeg to dvd files --- I believe these can all be used portably.