In your budget, the only type of 27" monitor you can get is a 1080p one. I would stay away from this, however, since 1080p at 27" starts to look somewhat blurry/ more like a TV. I would instead recommend a 24 inch monitor for its added clarity. If you want 27 inches, go for a 2560x1440 monitor.
Here's a good 24 inch monitor:
http://pcpartpicker.com/part/dell-monitor-m2gcr
It's 1920x1200, so 16:10 instead of 16:9. This pretty much gives you a few extra pixels at the bottom which can be used to view more of a web page, for example. Also, the monitor is an IPS one, so the colors will be superior to what you would see on a regular (TN) monitor/ panel.