If you have printers that doesn't come with a Linux driver, and Ubuntu doesn't provide you the correct driver to print with them, you can try the PPD alternative.
I've successfully printed on a Ricoh Aficio SP C410 that doesn't print correctly with the drivers that comes with Ubuntu Gutsy.
Ricoh doesn't supply the Linux driver but you can download the Windows Postscript driver installation. Launching the .exe with Wine will expand the installation files in a temporary folder. Here you can find the necessary .ppd files. Now, in Ubuntu, you can install your Ricoh printer with the Postscript .ppd files.
This solution worked well for me and I think it could work for a large set of printers.
Remember: Postscript is your friend.