I just got an iPad from my company for work! I can do pretty much anything with it that I want for the time that I have it, though, and am already totally geeking out over some free apps I'm trying out. So far, I've got a couple PDF books in iBooks, the free versions of the New York Times and The Economist, Words With Friends (play me!! send me a PM!), and an alarm clock.
iPad (and iPhone) users, what other apps do you recommend? I'd prefer to stay with free/cheap apps at the moment, but if there's something that's really awesome, I might consider spending more. I'd be particularly interested in anything related to productivity, science, classic games, music, news, fitness/health, and apps that you never realized you absolutely needed until you got them. Also, any tips for utilizing features the iPad already comes with?