Another vote for Hamrick's "VueScan"
Buy it once - lifetime licence. Windows, Mac and Linux.
Understands thousands of scanners, some of which so old that you wonder whether anyone is still using 'em. Regular updates for newer hardware as it appears. Brilliant customer service for problems (so I'm told, never had problems).
Interface is functional rather than beautiful and hasn't changed much, but boy do you get a lot of choices when it comes to control over your scanner!
One of really neat things about it is that you can scan multiple pages with PDF output and,
if you want, VueScan will just tack the last scan onto the first so you end up with a single multipage PDF.
One of the best and solidest pieces of pieces of software I ever bought - I never bother to install the lousy crapware-infested proprietary software that you get with a new scanner.
Mac
