Why are my iPad landscape screenshots rotated the wrong way?
This is default behavior and is not an issue with jailbreaking. Even my new iPad 2 straight out the box does this on 4.3. I see this as a bug and hope Apple fixes this.

The fastest and simplest iPad app that I've found that I like for rotating, cropping and flipping is called Crop Suey HD.

UPDATE: It appears as though iOS 5 has finally fixed this annoying bug. And the even better news is that they are now throwing in photo editing tools right in the photo viewer app; including the option to rotate.