There is no known viruses "in the wild" for Mac OS X. That doesn't mean there ever wont be. In fact, the dramatic increases in the market share of OS X means that we may become a target for malware sooner rather than later. However, the underlying security of the unix framework upon which OS X is build, combined with the low market share mentioned above, makes us a much more difficult and low value target.
So, for all intents and purposes, there is zero need for virus protection on OS X (same for spyware, etc.). However, it is possible to pass on files that contain viruses to other windows users. (i.e., if you receive an infected file on your system it is totally inert, but, if you send that to a Windows user on purpose - without ever knowing it was infected - it could infect them). So, for that reason, some companies require virus protection on their Macs as well. However, even then the usefulness is debatable.
Long story short, don't worry about virus or spyware protection. Crawl into the deepest, darkest parts of the Internet without a care in the world! (for now).