Portable applications suites are a great way to get your hands on a ton of useful software with minimal fuss. Got a new flash drive, or maybe an old one you don't know what to do with?
Throw one of these suites on it and you've got an instant software Swiss Army Knife.
PortableApps.com - John T. Haller's project is the most well-known suite on the 'net. It includes Firefox, OpenOffice (or AbiWord in the light version), Pidgin, Thunderbird, Sunbird, Sumatra PDF, KeePass, and more. Haller is very good for keeping the core up-to-date - you'll usually see new versions of the Mozilla apps the same day they're released.
LiberKey - The Ultimate version will take up half a gig on your drive, and it's packed with useful programs, including technician favorites like CPU-Z, RegShot, Revo Uninstaller, Unlocker. There are also loads of multimedia, networking, and internet apps. The 180Mb basic version is a lot like PortableApps with the addition of Piriform's tools (CCleaner, Defraggler, Recuva). They've got a handy comparison chart posted as well. One omission worth noting: OpenOffice.
Lupo PenSuite - In addition to a giant list of portable applications, Lupo also includes links to popular web-based apps like Flickr, G.ho.st, PixIr, RTM, Virustotal, and Zoho. Though, if you're using a portable browser you likely have all your favorite web apps bookmarked there anyway. If you don't need the full 300Mb, there's also a lite (90Mb) version which is like the PortableApps core with several technician's tools bolted on.
As noted by LOC in the comments: "The Lupo PenSuite does have a page with links to many other portable
or slim install browsers such as Chrome and Opera etc. (Also, CrazyBrowser and other lesser known browsers)" - Thanks!
WinPenPack - WinPenPack offers five different versions. There's the mammoth 2Gb Ultimate version (not every portable Windows application ever, but close enough), 370Mb essentials, and packs tailored for students, gamers, and web developers.
I was a little surprised to see that only one of these (Lupo Full) includes a browser other than Firefox (it includes Opera as well). For Chrome on the go, you can download Carsten Knoblauch's portable version or SRWare Iron portable.