ABBYY Finereader is easily the most accurate I've ever used - but thats a very limited sample! However it does have a good reputation
Old or cut down versions are often supplied free with scanners
OCR software for text recognition OCR PDF features - ABBYY FineReader
If you already have a scanner, you'll probably find you already have some bundled OCR software
edit
PS - something just remembered
The Open Source "Tesseract" program had a good reputation also, though I've never used it
https://code.google.com/p/tesseract-ocr/
Another Google project