As with every component of your PC system, the type of monitor you should get depends on what you’re going to use it for. I use mine for writing, gaming, and some light photo editing--all areas where IPS panels excel. In general, I think most people should get IPS monitors for their primary computers, unless you’re really into 3D gaming or play a lot of competitive first-person shooters.
If I were buying a new monitor today, I’d get one of two things: either a 24-inch, 1920x1200 IPS panel from Dell or Asus, or a 27-inch, 2560x1440 IPS panel from a Korean vendor. Here’s why, and what each of those options represents.
Your new monitor should have a resolution of at least 1920x1080, or 1920x1200 if you can get it. 1920x1080 is standard 16:9 aspect ratio and it’s the same resolution as an HDTV, so you can watch Blu-Ray and other high-def content at its native resolution without letterboxing. It is the ideal media resolution. 1920x1200 panels used to be more common in computer monitors. These have a 16:10 aspect ratio, and many people who work on computers find the extra 120 vertical lines handy, because they let you fit more information--like text on web pages and photos--on the monitor. I’d personally get a 1920x1200 monitor over a 1920x1080 monitor if I could.
A mid-range graphics card like a GeForce 660 Ti is more than enough to run a single 1920x1080 monitor at high quality settings for most games.
For a 1920x1200 panel, you really don’t need a monitor bigger than 24 inches diagonally. A 27-inch 1920x1080 panel has the exact same number of pixels as a 24-inch 1920x1080 panel; the 27-inch is just bigger and much more expensive.
Not to be constrained by standard aspect ratios like 16:9 and 16:10, Dell, Philips, and LG have introduced monitors based on the same 21:9 aspect ratio 2560x1080 panel. The Dell UltraSharp U2913WM, ($700), LG EA93 UltraWide (not yet released), and Asus MX299Q ($600, not yet released) are all IPS panels with a 29-inch diagonal. The panel makers say the aspect ratio is great for watching movies without any letterboxing, and a wider screen is certainly better for multitasking, but for the money you can get a 27-inch 2560x1440 panel and get more usable vertical space in a 16:9 aspect ratio, which has wider application and gaming support. Or you could get two 24-inch 1920x1080 panels, though then you'd have to contend with a bezel in the middle of your workspace. The 21:9 panels could be an interesting alternative to dual-monitor setups for some people, but I'd stick with the 27-inch 2560x1440 panel and get more screen real estate for the same price.