A free program for iPhone, by Pranoy Chowdhury.
The best way to learn to read music is to do it. Playing an instrument helps a lot as you get to read music notation. This is because you have to concentrate on the note you are playing, rather than looking at the sheet music. This app allows you to do just that, by listening to the note you are playing, and then guessing what the notation might mean.
The graphs in this app show how fast you are reading. If you spend more time thinking about a note, it will show up on the graphs as a positive value.