This is a freeware that list the heavy folders and their type on your computer. It also allows filtering by drives or folder types and re-scanning that takes less than half the time.
This app is portable and requires no installation.
Even Mac OS X risk infection by viruses. Published on the website of the company, where Apple recommends its users to use antivirus. There are suggested three commercial antivirus products, perhaps remember that are also free solutions as ClamXav.