Ok there are three options for you. (basically buy in your price range according to brand and certain specifics.) TN panels are the most common and in my opinion best for gaming in terms of response time and lowest input lag
IPS panels have B E A Utiful colors but have been known to have slight input lag
60hz vs 120 hz. 60hz is the standard right now, and if you arent pushing games well beyond 60 fps, don't go 120hz. If you have pretty much any card over a 760 or 270x, i would recommend a 120hz monitor for first person shooters if you have a more powerful card. (benq has the best 120hz monitors right now)
The three major gaming brands are
1. Benq. They are very well built and definately the lowest response and input lag of the bunch. You will undoubtedly have the highest kd ratio with this monitor (won't be a huge change but it will be higher if you are a fairly consistant player. The only thing these monitors have as a drawback is slightly worse colors than the rest, though even still it's not that bad and can still look really good if set up right
2. Asus makes the best all around monitors that are trusted by many gamers. The colors are slightly better than the benq, and they have low response times and input lag, get these if you play all kinds of games. When i say the benq monitors will give you a better kd, i mean literally you may get one extra kill every 100 kills due to the lower response time than the asus. (almost un-noticable to a lot of gamers)
3. LG makes an absolutely beautiful panel, and is the best looking of the bunch, but is not so geared towards gaming.
Make your choice and find the monitor that is in your budget. Also make sure to read reviews for yourself, and maybe go look in store (memory express, ncix, or other actual pc gaming stores (can be found anywhere, though prices may vary).