I have a Fujitsu ScanSnap which is quite heavily used, and I can't recommend it enough. Set up, stick some paper in, hit the big green button and it feeds through a pile of paper scanning both sides and out come OCR'd PDFs. Can't really fault the hardware or the software and it is very fast.

You can get the S1500 (Windows) for £299 +Tax in the UK and is does 20ppm duplex.

Just having a look around, looks like they have a Networked one as well! Pretty cool. It has what looks like some kind of big tablet style touchscreen on it and looks like it can dump PDFs/JPGs/TIFFs to a network share, FTP, SharePoint, Cloud, Email, Fax, Printer... and the option of buying the SDK! All for the low low price of 4x the S1500.