Windows only: QTWeb, a WebKit-based browser, is seriously speedy, doesn't let its interface get in your way, and can blend into any Windows theme. More than that, though, it has a quick-fire privacy mode. The browser does most of the stuff you'd want from its portable, no-install-needed executable, including password-saving, tabbed navigation, and plug-in compatibility. The real reason you might use QTWeb over, say, a portable version of Firefox 3.1, is its built-in, quick-access privacy mode, if you want to browse on someone else's system (or your own) and not leave a trace. Firefox 3.1 may have a built-in privacy mode, but if you're looking for a slimmed-down, no-add-ons-please browser for on-the-go browsing, QTWeb's a great choice. QTWeb is a free download for Windows systems only; make sure to grab the "stand-alone executable" if you're going the USB route.