UNO HD for iPad [$4.99 - iTunes link] by Gameloft brings the classic card game to bigger, bolder life on that 9.7" screen. At first blush, UNO more so than something like NOVA feels like it could have been a universal binary, sparing existing owners of the iPhone version from having to buy it twice. However, Gameloft wisely upped the anti based on the iPad's-size, offering a 4 player option that makes it eminently more suitable as a true board-game replacement -- you can realistically sit 2 or 4 people around an iPad and start up the multiplayer version of the game, share the screen, and get your UNO on.
You can of course also use single-player mode, or multiplayer between devices either locally or online. The graphics look prerequisite-ly great on the iPad, though we did find the controls a tad challenging (choosing and playing cards weren't quite as buttery smooth as we'd like).
A side effect of the game being run on an iPad instead of with real cards is that it's almost impossible to make mistakes or (gasp) cheat. The game only allows you to play cards you're allowed to play, when you're allowed to play them. Whether that's a good or bad thing we'll leave up to you and your consciences to sort out.
If you like UNO and you want to bring a little bit of real world social interaction back to your family and friends, grab an iPad, fire it up, pass it around, and let us know what you think.
Video of me taking on a challenger, after the break!