Apple released the next big update for Leopard today, 10.5.2. There's also a security update for users running 10.4 Tiger, Security Update 2008-001. Security updates for Leopard are included in 10.5.2 while tiger will have the 2008-001 as an update.
Mac OS 10.5.2 includes updates for Airport, Back to My Mac, iCal, iChat, Mail, Printing, Safari, Time Machine, and much more. The security update includes fixes for Safari, Mail, Parental Controls, Samba, Terminal and X11.
Here are links to more information about the
Leopard 10.5.2 update and
Security Update 2008-001. To get these updates, click the Apple in the top left of the screen and select Software Update.