Gutenprint (formerly called Gimp-Print) is an open-source package of improved printer drivers and utilities that can be installed on Mac OS X to enhance printing functionality and add additional support for older printers. It has driver support for over 1300 printer models, and adds a GIMP plugin for better print customization and color adjustments.
Since I do a lot of Mac system imaging and deployment, I don't like to install a bunch of separate print drivers on a seed image. I initially just used Leopard's built-in generic Postscript or PCL driver, but I had many issues with printing speed (the speed of spooling and job submission, not the speed of the physical printing process) and print quality. So I installed the Gutenprint package, switched all printers to the Generic Gutenprint PCL driver, and the printing issues subsided.
To use Gutenprint, simply download the .dmg (5.2.3 is the latest version) and install the package. All of the necessary PPD's and drivers will be copied to your computer, and you will be able to select Gutenprint drivers when adding printers. If you have an Epson Stylus Inkjet printer, you will then also be able to use "escputil" from Terminal to do printer maintenance like head aligning and cleaning.
Update: Thanks to Charley and Olligarski for commenting that Gutenprint drivers are now included in Leopard. I have used Gutenprint for a while but failed to check if it was installed before I started using the package. It's still worth the install if you're a Tiger user, but the latest version requires at least 10.3 Panther.