This is the best virus check for Mac OS X I've seen. I did encounter some issues with it. I gave it an extra star for being an free open-source application.

Pros: Great free product, thorough.

Cons: Scaning seems to permanently hang at times, but doesn't cause application crash. Unable to quarrantine a specific virus-laden message packed in an .mbox file, but at least it can inform you of virus existence. Update feature or versioning is broken (I am running version 1.0.1 but the update feature still triggers and tells me that a new version of either the application or the engine (not specified which) is available, whereupon visiting the download page I find that the latest version is 1.0.1).