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.