[atmosx]

Isn't clamAV[1] very good at this already and free of charge AND not keen to close an eye on specific signatures.

[1] http://www.clamav.net/doc/install.html

[2] http://www.clamxav.com for OSX

[niels_olson]

I believe Cisco now owns clamAV.

[edwintorok]

You don't have to use/trust the official database (or its whitelist). You could create a custom database with just the signatures you are interested in and run a scan with just that.