Ant & Phing
Julien, who is a super genius, has a write up building apps with ant, including the all important concatenation of js and css files. In my experience a shocking number of people working on web apps have no build process beyond “copy the files to the server”. Tools like ant make it easy to deploy.
Wait…what if I think java is the devil and prefer PHP? You are in luck, because Phing is the same thing but for PHP. Even better, it includes phpunit testing tools.