I don't know an app to do it, but if you're willing/interested in installing the SDK on your computer, you can use that to take screenshots of your phone. I was impressed with the quality/size.
going through the sdk, as thecatwasnot mentioned, is the only way to do screen caps non-rooted. its a pain to set up initially, but once youre good to go, its super easy to use. its how i used to cap my OG droid back in the day when i was too scared to root