No doubt, the last few years have been pivotal in driving the cloud security phenomenon. And there doesn't seem to be any sign of a slowdown in 2010. Driven in part by the tough economy, cloud solutions took off over the last 16 months with an onslaught of SaaS acquisitions by some of world's largest security players. Symantec was one of the first to get the ball rolling with its acquisition of MessageLabs in October of 2008, followed by acquisitions by players such as WatchGuard, McAfee, Barracuda, M86 and Cisco. In addition to cloud-based antivirus, spam filters and Web scanning engines, security companies are now launching cloud-based DLP and authentication and log management technologies. Here are our picks for the coolest cloud security vendors helping to foster the SaaS phenomenon and drive it forward in 2010.