Edit: or you can go with the above lol, I'm not recommending too many specifics in mine, just the way to go about shopping
http://au.pcpartpicker.com/
use this site as your resource, you can compile parts on it in system build, you pick individual parts according to your price point/liking, and it will tell you which retailers/e-tailers currently have the product in stock and at what prices, it will automatically update to use the lowest price of any retailer available.
For a base machine you will need:
CPU
Motherboard
Storage
Memory
Video Card (integrated graphics are obviously not enough)
Case
Power Supply
Operating System
the rest is up to you, you don't NEED an optical disk drive, since you can always boot your computer from a USB, however it's generally recommended that you get a cheap one. CPU coolers are not a necessity since CPUs usually come with a stock, but if you want to overclock your system, get one. Case fans are optional but recommended if you know what kind of cooling you want/need, cases usually come with 1-3 fans themselves but a higher quality one never hurts. For keyboards, mice, and headphones you should consult other people/sites rather than use the part picker.
sound cards are generally considered luxury, and may not even fit on your mobo if you are on a tight budget. Wireless adapters are cheap but usually unnecessary because desktop.
Now, down to the nitty gritty:
CPU - you have 2 choices, AMD or Intel, AMD is generally recommended for budget buyers because of their incredible value, but Intel takes the cake in performance. If you want to run the latest and greatest games, I recommend at least an FX 6300 or above for AMD, and an i5 3330 or above for Intel. The FX 6300 has weak single thread performance but has 6 integer cores, is unlocked, and loves to be overclocked, can reach i5 performance with enough of an O.C. i5's have really strong single thread performance but is limited in multi-threaded apps (multiplayer in BF4 would be an example), but they are still very strong processors, the i5 3570k and the i5 4670k are considered the sweet spots of gaming today because of their strong performance and overclockability.
Motherboard - rule of thumb: you get what you pay for in a motherboard. Do not cheap out on this component, a bad one will be the end of your system. I generally recommend brands that use solid parts for their mobos like Asrock and Asus, though some research on sites like
http://www.overclock.net/t/1144067/amd-990x-970-am3-motherboard-buyers-guide-help-thread will be very helpful.
Storage - 1 TB is usually what average consumers go for nowadays, it's a good amount of storage for usually good prices, go Seagate and Western Digital, solid brands.
Video Card - the minimum you want to do for these sorts of games is Nvidia Geforce GTX 660 and AMD Radeon HD 7870, good brands include Asus, Sapphire, MSI, EVGA. Powercolor often has killer deals but questionable quality.
Case - watch the reviews is all I can really say, this one is most up to preference out of all parts. Do not go for bells and whistles in cheaper boxes, instead look at what features you need and which cases fit those requirements.
Power Supply - an EXTREMELY important part, do not go cheap here either,
http://www.eggxpert.com/forums/thread/323050.aspx
this is a good guide on what to look out for, do not go under tier 3 is my general recommendation.
If you want a CPU cooler, a cooler master hyper 212 Evo will likely be the way to go, you cannot beat it's value.