osX for the past few years has been losing all the exploit tests at the big security conferences but their market penetration doesn't make sense for malware, of which the point is to infect the most computers possible. It's a matter of market targeting more than os vulnerability these days. That said, as osX is increasing in share, effective new malware on the platform will become increasingly common.
For solutions, Kaspersky is available for osX as is Avast! and there's also Sophos. The main osX threat are trojans and all three do pretty well against that type of malware.