How can I enable fingerprint authentication on a Mac? What compatible scanners are available?
Yes - you will want to start with the Smart Card services source code or compiled installer that Apple publishes and then pick whatever device you like that integrates to this infrastructure.

Here is Apple's starting point and a few more links that may help you in your search for a biometric authentication solution:


http://support.apple.com/kb/PH10872
http://www.cac.mil/common-access-card/managing-your-cac/
https://www.dmdc.osd.mil/smartcard/owa/ShowPage?p=faqusers#fingerdeers
http://www.cacsecurity.com/biometrics.asp