I currently own a Toshiba tablet (don't know the name, but it's one of the first models, 10 inch screen, and very very thick) and I'm looking to upgrade to a better tablet because of how laggy this one is. The main things I'm looking for:
1. Good for reading eBooks (pdf, epub, mobi etc.) I have a very large eBook collection that's mostly in pdf, but my current tablet is very laggy when it comes to page turning. If I try to turn too many pages at a time the app will even shut down. If this is an issue with my app and not the tablet, then I'm currently using Aldiko for my reading app.
2. HD Movies. Again, my tablet is generally pretty laggy when it comes to watching HD movies, especially when they're in MKV format or if the file size exceeds ~3 gb. I use either MX Player or BS Player free for my apps.
3. Attachable Keyboard. If there's an attachable keyboard accessory available, especially in the form of a case, that's a huge plus.
4. Large Screen. Just looking for a decent size screen here. 10 inches should be fine.
Thanks a lot!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic