I prefer 1 monitor that is as large as I can stand to look at. I currently use an Asus 25.5" with a 1900x1200 resolution. Charts sure look nice on the big screen.
I've also used 2 monitor setups before which can come in handy (i.e. leave all your instant messengers running in one window). I've even used 4 monitor setups before. The extra monitors on a 4 monitor setup can come in handy sometimes when you need to watch a lot of stuff but most of the time all those extra screens are just wasted space. It will give you nice bragging rights though when friends and family come over.
I've also used 2 monitor setups before which can come in handy (i.e. leave all your instant messengers running in one window). I've even used 4 monitor setups before. The extra monitors on a 4 monitor setup can come in handy sometimes when you need to watch a lot of stuff but most of the time all those extra screens are just wasted space. It will give you nice bragging rights though when friends and family come over.