Apple's iPod Touch is just fun to use. While it is marketed as an MP3/Video player, I think the Web Browsing and additional functionality through the "jailbreak hack" are even more enticing.
The interface is very intuitive, and while it may not be the most efficient method for browsing/searching for movies and music, you don't really mind because it is so fun. As usual, Apple is very particular about what types of video and music can be played on it's devices, but if you're willing to put in the effort, there are lots of great apps to help you convert your videos to an iPod compatible format. Of course, if you've got the cash to buy content off the iTunes store, that's definitely the easiest approach. I've also started loading content from huge collection of free video podcasts -- this gives me something random to watch while I'm in line at the grocery store...
I haven't really used the iPod Touch enough to speak to its battery life, but from what I've heard from other user's experiences, you should have enough battery life to watch videos throughout a flight from Los Angeles to New York... just be ready to plug in when you land.
The biggest knock against the iPod touch is that it seems you might just be better off getting an iPhone so you can enjoy the wireless browsing wherever you have cell phone reception (rather than relying on WiFi connectivity). Also, the iPhone has a built-in speaker, where the iPod touch requires headphones.