I know lots of newer setups can do this already, but if you operate in prehistoric cheapie mode like I do with my home system, this <img src=/S/free.gif border=0 alt=free width=30 height=15> tool looks good on first trial.
The Code Project - Scan2PDF - Free Tools
You need to be registered though, to download from the site. (I have been for years, and receive no mails other than their newsletter that I requested).

I've tried combining this with Pdftk commandline utilities and have managed to generate multipage PDFs straight from scanner. I'm thinking of a simple drag/drop GUI to further enhance the process.