The evidence comes from an image found in the latest beta. The image (homeScreenOverlayFaceTime~iPad.png) is used to preview home screen wallpaper changes, and clearly shows icons for the Camera, PhotoBooth and FaceTime apps. The current image found in iOS 4.2 does not have these icons.
The PhotoBooth app is an interesting addition, PhotoBooth is a Mac OSX app that lets you take photographs and video. You can then apply filters to create fun images and videos with different effects and backdrops and email them straight from the app. FaceTime will allow iPad 2 users to video chat with iPhone 4 users, latest gen iPod Touch users and Macs.
So that pretty much confirms the camera story, not that we needed any further confirmation; what is still left up in the air, is how many cameras the next iPad will have. One or two, what do you think? Let us know in the comments!