CheckMate for Mac

From Brian R. Hill:

Checkmate is a preference pane for MacOS X 10.1 or higher that allows you to generate and compare secure MD5 checksums of critical files. This can be used to detect whether these files have been altered by viruses, root kits, trojan horses, or other possibly malicious programs.
Checksum validation can be run manually from inside the preference pane, and/or scheduled to run hourly, daily, weekly, monthly, or each time you restart.
If the validation process finds any files whose checksums don't match the values stored, several notification options can be triggered, including a popup dialog and email. In addition to the default list of files that are included for validation, you can easily add and remove additional files that you wish to validate.
You can also export the list of file checksums to a file to be stored somewhere other than the computer it was made on (such as on your iDisk). You can later load this externally-stored file back into the preferences panel to verify that the checksums themselves haven't been altered.
NOTE: The choice of files that are checked by default was derived by examining a number of other file system checksumming (or tripwire-type) systems on other UNIX-like platforms. If you believe that there are other OSX-specific files that should get checked for malicious alteration, please send me your suggestions for possible inclusion.