You can now download Mac OS X 10.4.3 through Software Update.
You can read about the updates here (Apple.com) and the security updates here (Apple.com).
Some of the updated areas:
* AFP, SMB/CIFS, NFS and FTP networkÃŠfile services
* AirPort and Bluetooth wireless access
* Core Graphics, Core Audio, Core Image, and RAW camera support
* disc recording when creating and burning media
* .Mac sync services
* Spotlight indexing and searchingÃŠ
* Dashboard widgets: Dictionary, Flight Tracker, Stickies, and Unit Converter
* Address Book, AppleScript, Automator, Dictionary, Font Book, iCal, iSync, Mail, and Safari applications
* Disk Utility, Keychain Access, Migration Assistant, and Software Update
* compatibility with third party applications and devices
* previous standalone security updates