Apple released Security Update 2010-001, an update for Mac OS X and Mac OS X Server, versions 10.5.8 and 10.6.2. The update addresses several key security issues, including issues with maliciously crafted MP4 audio files (AAC), an issue with printing-related cupsd, issues dealing with TIFF and DNG images, and an issue that could allow the bad guys to capture data sent by your Mac across a local network.
There is also a forced update for Adobe Flash to address issues with that technology. You can read more at the above link.
The update is a 22.4MB download for Intel Macs running Snow Leopard, and is recommended for all users.