I'm personally fond of a new Dell Ultrasharp U3014 monitor I got several months ago. I have a video card a couple of years old - an ATI Radeon HD 7850 with 2GB VRAM, and it drives the big 30" monitor as well as my two older 20" monitors turned up sideways perfectly, to make a Photoshop editing station that's potent. All the various Photoshop panels are on the sides, and the entire central monitor is available for the actual editing.
As far as computers go, I've yet to find a machine better for Photoshop work than a Dell Precision Workstation. Others will of course have their own opinions.
It's possible to find off-lease workstations, such as the Precision T5500 system shown above, being sold used on eBay by refurbishers. Depending on who you choose you might even get a Dell warranty (I did). Their newer T5600 line is current, which makes the just off cutting edge systems cheaper. You can score a good deal this way, but you need to educate yourself very well on the options before choosing a model with particular set of features. Another member on here (JJMack) got a good deal on a Precision T5600 refurbed from Dell direct. I hope he chimes in and describes his experience with his T5600.
Some things to think about:
- SSD storage is greatly preferable over HDD storage, and is well worth the additional cost. Do not skimp here. Get more than you need. Consider building a RAID array of them.
- More RAM is better, and much more is much better.
- A good balance between individual core speed and core count is needed. Too much of one and not enough of the other isn't as good.
- If you want multiple monitors, a single modern video card that can drive multiple monitors is essential; don't try to run Photoshop with multiple video cards.
Two general observations re monitors, without going into specifics:
1. A monitor is basically an analog device, so quality has direct impact on your work. Not like a CPU, where a cheap one does the same job, only in a little longer time. You get what you pay for. Expensive monitors are expensive for a reason.
2. The one single biggest cost factor is panel size. On a budget, go down in size, not quality. A good 24" is way better than a mediocre 27", at the same price point.
And I should perhaps add the basic quality parameters, the ones that matter (don't pay attention to the marketspeak nonsense, like "dynamic contrast ratio" and so on):
- Good and even tonal response without obvious banding or stair-stepping.
- Good separation into black and white. You should be able to see at least level 3 against black; and 253 against white.
- Panel uniformity from side to side and corner to corner, both luminance and color. Problems here can't be calibrated away.
- Wide viewing angles. IPS and PLS panel technologies give you that, TN does not. Most consumer-level monitors are TN-based. Avoid those.
Optional, not essential but a big bonus:
- Wide gamut. Note that this carries some implications that you must be aware of in terms of color management. Failing that, wide gamut is just asking for trouble.
- The possibility for hardware calibration directly to the monitor, not the video card. This often takes the form of a dedicated calibrator sold with the unit.
- 10 bit capability, which will give smoother gradients (1024 levels instead of 256), if the rest of the hardware/software supports it.
By the way, here is a great site.
Read a few reviews to get a feel for what's important.
Oh, and one other thing... Though the marketing may be attractive, the time may not yet be right to get a high dpi monitor (e.g., a new 4K model). The software is not all yet mature enough to use the higher resolution properly.