I'm especially curious if someone has tried an ultrawide such as the Dell U2913WM? It looks like an interesting setup for programming but then again it might not be. I find 2x 23" widescreens too wide for comfort so it might hit the sweet spot.
After all that, I would say, go as big as you can. Going to at least the 2560x1440 27" monitors can make a huge difference. If you can go all the way to 30", even better. Personally, my first choice (aside from waiting for a 30" 4k monitor) would be 2x 30", followed by 30" + 24", followed by 27" + something (ideally, another 27").
An early image of my setup is here: http://www.otakunozoku.com/my-new-monitor-layout/
I used to spread my workspace over two 21" monitors, but now having everything on one large monitor is much more comfortable.
Not sure what I'll do with the other two monitors. Maybe kludge them into a nightmare all-in-one with an old laptop.
When I get home, I hook my 11" MacBook Air up to it. Portable when it needs to be. Tons of screen real estate when I need it.
The horrible thing is that I actually find myself wanting more screen space, now and again. (Part of that might be using 16pt Consolas as my emacs font, but I work with so many people who need glasses.)
At home I have a single Dell 24" IPS monitor, used for photo editing and lighter coding, in addition to general home usage.
I would love to switch to 1x 30" 2560x1600 and 1 20" 1600x1200 pivoted.
More and more thinking I may be better served by a single 27" or 30".
3 * 24" for media.
2 * 16" portrait mode for coding.
1* x120e laptop for work.
1* macbook pro to look pretty in public.