Scan lot of documents and output them in PDF
Two answers:

1) By far the easiest/best document scanner for Macs is the Fujitsu ScanSnap series. You just insert a stack of papers, press a button, and out pops a PDF. It scans both sides of each page in a single pass.

2) To convert a scanned PDF to something searchable, by far the most reliable OCR program available (for any platform, Mac included) is the AABYY FineReader package. It is miles ahead of any other package- especially Adobe Acrobat's built-in OCR which is barely usable. This comes bundled, at no additional cost, with the ScanSnap, or you can buy it separately.

I've used one of these for several years... have scanned all of my old bills, receipts, documents, etc. so whenever I need to find something I just use spotlight and can find it in seconds.