Since your monitor is the portal to actually using your PC, it makes sense to invest in a good one. Of course, the best gaming monitor for your needs depends on how you use your PC, and if ultra-fast framerates is your thing, check out this deal on the Alienware 25 (AW2518H).
This isn't very big at 24.5 inches, and the resolution stands at just 1920x1080. However, that makes it easier on your hardware to utilize the rapid native 240Hz refresh rate it offers, making this a great choice for less demanding esports games (Counter-Strike: Global Offensive comes to mind). And as for the size, not everyone has the space for a hulking display.
As you might have guessed, the AW2518H is built around a TN panel (240Hz refresh rates are no longer the exclusive domains of TN displays, but IPS monitors are much fewer in number). Compared to a typical IPS display, TN panels have tighter sweet spots and lower color gamuts, so keep that in mind.
While professional photographers will want to look elsewhere, competitive gamers have reason to zero in on this one. It has a 1ms response time to facilitate quick reactions, and is built for speed and smooth gameplay. To that latter point, it supports Nvidia's G-Sync technology with an actual G-Sync hardware module inside (as opposed to being a "G-Sync Compatible" model).
The AW2518H is also fairly generous in terms of connectivity. The underbelly is home to an HDMI 1.4 port, a DisplayPort 1.2 connector, two 3.5mm jacks (headphone and audio out), and four USB 3.0 downstream ports.
