Another iPad vote here...
Light, portable, instant-on, high battery life (10 hours) device for general browsing, playing games, watching videos, etc. A lot of the time there's no point in me firing up the desktop, I can just use the iPad. It's just...
convenient.
My wife was very sceptical when I bought mine six months ago... Now she has her own!

Again, similar uses. She lugs her laptop and netbook around
a lot less now that she has an iPad.
More convenient for travelling too. We went to London on my birthday a couple of weeks ago, and both took our iPads with us. Two player Scrabble on the train there, videos on the way back. Much better than trying to watch videos or play games on a smartphone while travelling, and a lot lighter and portable than a laptop. I took mine to Blackpool a few months back (as did a few others here

). Five hour train journey from Cambridge. Perfect for videos, games, and web browsing while travelling.
iTunes format (.mp4) videos will obviously play natively. For anything else, e.g. xvid/divx within the .avi container, or H.264 within the .mkv container, I just use
AVPlayerHD...well worth the £1.99 cost. I also stream from my PC to my iPad using AirPlayer, which will stream from UPnP/DLNA media servers.
---------- Post added at 20:50 ---------- Previous post was at 20:48 ----------
But if you do go for a tablet other than the iPad, go with Android, and avoid Win7.
The EeePad Transformer is meant to be good, and the Moto Xoom has had quite a price cut after failing to sell very well at all. Be aware though that there are fewer tablet-optimised apps available on Android.