Tesseract - Tesseract is an optical character recognition engine for various operating systems
TinEye - Reverse Image Search to help find an image's source, duplicates or altered versions.
Onlineocr.net - Free Online OCR service allows you to convert PDF document to MS Word file, scanned images to editable text formats and extract text from JPEG/TIFF/BMP files
GImageReader - gImageReader is a simple Gtk/Qt front-end to the Tesseract OCR Engine.
ABBYY FineReader - ABBYY's latest PDF editor software, FineReader 16 you can easily convert files like PDF to Excel, PDF to Word, edit, share, collaborate & more with this PDF editor!
Yandex.Images - search for images on the internet, search by image