We use the Hudson buildbot for for big Java web app building from ant build scripts. Hudson is pretty sweet for our purposes. It has a master/slave setup so builds can be done concurrently (on a timer or on-demand). Slave nodes can be any OS/hardware combo provided it has the needed build tools already on it and is on the network (and won't crash every 10 min).
Full web-based interface including live console output, change logs, artifacts from the build are available across the network including previous builds (if successful). Awesomesauce!
