Icognito, as the name implies, allows you to surf the Web without leaving any sort of history. Let’s not kid ourselves: it’s for porn. Go nuts. It’s $1.99.
WebMate implements a “light” version of tabbed browsing. Rather than open each separate link in a new tab, WebMate queues the links. When you’re done reading site one, you merely click (or whatever) and site two pops up. $0.99.
And there’s others, obviously.