CSS Browser Selector
Rafael Lima took inspiration from 37 Signals browser selector idea and created it. “It” being a JS library that allows you to create browser specific CSS to be merged into your normal classes.
You can prefix browser specific elements (available codes: ie, gecko, opera, konqueror, safari) and the library will make sure that the correct items are added in for a particular browser.
This can be considered cleaner than some of the really ugly hacks that you normally face.