Microsoft OneNote has a built in scanner, also Samsung stock camera app will recognize if a photo you're taking is a document and crop in on it automatically.
Update: I stumbled upon the Samsung stock camera doing that yesterday. I was taking a picture of a interesting sign and it a put crop/scan box around it. I tried it again with a magazine cover but it wouldn't do it. I think lighting was a factor though. I'll have to test it since more.