A 1920pixel-wide monitor is 274 characters wide (if your characters are 7 pixels wide, like mine). That's two files side-by-side with 100 character lines, or three files side-by-side with 80 character lines.
I usually work with a file list/project navigator/something to the left and a build window at the bottom of the screen. I usually have two screens so that docs/browsers/whatever can live on the second screen. Seems to work for me.
In my current project I'm using eclipse which has a right-hand panel for build targets. Even with both left and right hand panels there's still enough space in the source window for 130 character lines.
Don't get me wrong, I think most lines should be short and that you should endeavour to keep them a reasonable, readable length. I just disagree with 80 as a hard limit.