I just got my fourth monitor. Two of them are old shitty 900p screens though. My main displays are my new 144hz 24" 1080p panel ($160 black friday sale) a 21.5" 1080p panel over hdmi, and the two shitty old panels I got from clients throwing out their old screens.

Usually the layout is IDE on the main window, docs on the second screen, IRC, git, and github on the third / fourth.