So, my brother and I want to get into PC gaming. I've got my rig selected (FX-6300, Radeon HD 7850, ect.), but my brother doesn't have a clue what to get.
He is on a $550 budget, and he also needs a Mouse, Keyboard, and Monitor (1920x1080, LED, speakers built in).
So, try to get the best performance for under $550. (He wants to play games like CS:GO, Civ V, and Burnout/Need for Speed.)
This is a little under budget, but includes everything you asked for. It is an APU based system with very fast ram for increased game frames per second. I think it will serve well and will be upgradable easily. Just get a new graphics card when you can. Games will will still be playable at 1080p. The CPU and other parts will be good for a few years.
This also has a decent gaming mouse. The keyboard is basic, but I don't think that is as important as a good mouse. The keyboard is still a quality build, but its a basic typing keyboard.
http://pcpartpicker.com/p/1zvny
Also, if you have a HDD already, then you could invest in a 64 gb ssd to install windows on and speed up the system.