Three displays, center one 2560x1440, with a pair of 1920x1080 in the wings. Three different display qualities (cheap Envision, decent Samsung, Korean IPS) so I can accurately see the differences in colour reproduction (avoiding a mistake a lot of Mac "designers" make only working on IPS then wonder why their shades of tan look like purple to everyone else).
I used to make room for a music stand to prop up reference books on, but since most things have moved online or to PDF I don't bother with that anymore -- again the multiple displays making that easier to deal with. (and part of why Winblows 8 fullscreen only crapplets were a middle finger to usability)
The multiple displays makes it easier to have realtime chats going with the client, multiple code windows open side-by-side so I can see my back-end code/markup next to my CSS next to my scripting next to MULTIPLE browser windows for testing.. To that end editors and IDE's that use 'tabs' forcing everything into a single window are an epic /FAIL/ at development and a step backwards in functionality.
Since modern keyboards -- PARTICULARLY these flat useless chiclet crap that's all hot and trendy right now despite being the second coming of the PCjr or Sinclair Speculum -- are useless garbage, it's IBM Model M or GTFO, and for ergonomics sake and to avoid carpal I use a Logitech M570 trackball; the type where your thumb moves the ball and the remainder of the hand stays at rest.
IBM Model M. When you have to type every last {expletive omitted} character in ASCII7, accept no substitutes.
When it comes to keyboards I'm a bit like Al Bundy's opinion on toilets.
Bud, keyboards today aren't worthy of the name. They come in "designer" colours and they're too low. And when you type, they make this weak, apologetic sound. NOT the Model M. They only come in beige, and when you type on 'em? Ker-CLICK! That's a man's click Bud. A Model M says "I'm a keyboard, gimme your best shot!". Oh if only a Model M could talk the stories it could tell.
Part of why I cannot fathom how anyone can do serious work on a laptop -- on top of the near useless screen resolutions and sizes. I could ALMOST do development on my MSI laptop with its steelseries keyboard and 17" 1440p display... but it still comes up short compared to a 'proper' development station -- particularly at a comfortable distance.
Though I think posture and seating difference is someplace I differ from the crowd too. I watch people hunched over their desks or laptops, faces plastered inches from the screen and wince thinking "Isn't that killing your back? AND your eyes?"... I mean for me, inside three feet from the display is uncomfortably close; though that is probably ALSO why I don't run standard font metrics except in testing VM's. "8514 / 120dpi / 125% / Windows Large / Windows 7+ Medium / pick a name already" being the norm on my workstation. has been since windows 3.0, since I usually ran one notch of resolution higher than the norm as a "rich man's anti-jaggies".
Though that brings VM's into the picture, a must-have for testing even for web development given how OSuX and Linsux have different font rendering tech and font stacks from Winblows... so you HAVE to test all three. Just look at how firefuxxors renders different line lengths on Mac than it does Windows, or how Freetype makes all Linux browsers render the majority of font choices -- particularly webfonts like the incompetently slopped together Google font "raleway" -- as near illegible crap. NOT that it seems many others working on user interfaces seem to care about legibility anymore given the raging chodo so common now for illegible colour contrasts, goofy webfonts, and STILL crapping out pages declaring font-size in px!