Twain Sane doesn't appear to support my printer, so that's out.
I downloaded new drivers from HP which replaced HP ScanPro with HP Scan, which actually works. Preview and Image Capture also work, although they don't have the features of HP Scan, which is really okay, as my scanning needs are pretty basic.
Exact Scan, nice as it may be, is way too spendy for me.
Thanks all, problem solved.