Can someone suggest a couple free and good anti virus programs that work for mac.

There are no viruses that can affect an OS X System.

i use macscan
http://macscan.securemac.com/

seems to work well [free trial]

but again bobw is right

The two industry leaders are still Norton Antivirus and
McAfee Virex. There are still others out there. I would
suggest navingating to http://guide.apple.com/
usindex.html (or if you live elsewhere in the world, go to
http://www.apple.com and click the "Made4Mac" link on
the top of the page) and searching for Antivirus software
there.

As stated above however there is no real need for
antivirus software or spyware checkers on the Mac OS
because at the moment there aren't any. With the
combination of an UNIX foundation and the security
designed into the OS by Apple engineers the OS is very
secure.

Good luck!