I have one of the Apple covers and usually that is all I use if I am carrying it in a briefcase with a place for a notebook for instance. If not, I have cases from SFBags. I have had their cases for a number of computers over the years and they are first rate.

I have this one for the iPad with its cover on, although I originally got it for my iPad 1 which is bigger. They make a very similar one for iPad 2s


And this one for the iPad with cover and a Bluetooth keyboard.