Barnes and Nobles variation of the Kindle, the Nook, recently received an update with Nook Color. It also has a video player and some android apps. But Barnes and Nobles is not focusing on any of those applications, they are really trying to focus on the book experience. Internet browsing is also an option via Wifi, but don't call the Color Nook a tablet, even Barnes and Nobles doesn't.
But tablet does apply to Samsung Galaxy Tab, the Nook Color and the Galaxy Tab are the same size. But the Galaxy Tab is about $150 more with a 2 year contract. Those extra dollars bring you wireless connectivity, a camera, and android apps. Although you're getting android apps, this can be a problem, because the apps are made for smart phones, so they don't fully take advantage of the tablet's size.
Space is not an issue with the Apple iPad, the difference between a 7 inch tablet and a 10 inch tablet is actually about twice. The iPad makes the most of that extra space, you have a large surface to enjoy full color books.
With all things considered, here is our conclusions :
If you wanna read, get the Kindle. If you want to watch movies and do other sorts of things and read, go for the iPad. The Nook Color and Galaxy Tab are still great devices, but updated versions could make them better.