PhotoScore 6 Ultimate
If you're looking to turn your old sheet music into playable, editable MIDI or notation files, you won't find a more feature-complete or effective program than Neuratron's PhotoScore 6 Ultimate. Like rival Musitek's SmartScore, PhotoScore takes you through the entire process from scanning the sheet music, to editing the notation, to saving your music in a variety of file formats.
One unique PhotoScore feature that I found very handy is the alternate recognition engine for handwritten music. It performed much better on my old music class exercises than any musical OCR I'd tried to date. I wish it hadn't--my compositions weren't very good. The program is easy to use, though I could imagine a more intuitive interface. However, it works very well with a wide variety of music.
--Jon L. Jacobi