Instead of relying on third-party companies to develop and distribute drivers for printers and scanners, Apple distributes them itself as part of its open-source CUPS (Common Unix Printing System) technology that it has incorporated into OS X.
As part of this setup, as new printers are released by companies, Apple takes generic printer drivers and tweaks them to manage the features and options that the new printers have, followed by releasing packages of these drivers for users to download.
Today Apple released a couple of driver updates for new Brother and Lexmark printers, available for OS X 10.6 and OS X 10.7 from the following download locations:
Brother Printer Drivers 2.8 (149.61MB)
Lexmark Printer Driver 2.7 (182.93MB)
These downloads are relatively large, as they contain the printer drivers for a number of new and updated devices from these companies. If you own a Brother or Lexmark printer, then while you can download and apply these updates, you likely do not need to.
If your specific printer's driver has been updated in the package, then instead of downloading the package go to Software Update in the Apple menu and have that utility check for driver updates. Doing this will give you an update file of a few megabytes in size that contains the driver for your device only, instead of wasting hard-drive space by installing over 100MB of additional drivers you will not use.