Definitely 2 monitors.

I often have to review scripts - sometimes many, many scripts. Being able to have a file manager one one screen and SSMS on the other is a great help.

Or SSMS on one, BOL on the other, or SSMS and a web browser.

I've used dual monitors for years at home and wouldn't want to work any other way now.

Finally got a Tablet as well to replace the mouse at work. No more RSI.