As I have always said, great software is worth mentioning (and buying)!
Optical Character Recognition (OCR) software has always been expensive and unaffordable for most users. Now I have found a poor man’s version (unlimited usage free trial, and only $29 if purchased), yet it still yields very accurate results!
VelOCRaptor is a very easy to use OCR application for Mac OSX, based on an open source OCR engine. You just simply drag an image into the program, wait 10 seconds, then it’ll make most of the text selectable and you can save the document as a searchable PDF file. I tested it with a nice and clean scanned document at 600 dpi, and it came out to be almost perfect. The only things it has a little trouble recognizing are super-scripted words and apostrophes. I also read that strange fonts will be difficult to recognize, so stick with fonts like Times New Roman and Arial.
Of course this is not a high-end professional OCR software, but it can recognize enough words in the document that you can search for it in spotlight. Check out this demo video:
P.S. After you have created a bunch of PDF files, another great freeware to combine them into a single document is Combine PDFs.