Jeffrey Way has created an app which looks through your CSS and adds all the missing CSS3 vendor prefixes. It’s smart enough to do it right no matter which ones you’ve added or forgotten. Cooler, it has an API which allows you to it without ever leaving your favorite text editor.
Update: This app is dead. The biggest tool for adding vendor prefixes these days is Autoprefixer (available on CodePen as a tool!). You can also do it client-side with Prefix-Free.