I just thought I'd throw my $.02 in here on the build.
Case:
http://www.amazon.com/Rosewill-Gaming-T ... tower+caseCPU:
http://www.amazon.com/Intel-i5-4670K-Qu ... ords=4670kGPU:
http://www.amazon.com/GeForce-GTX750TI- ... TI-OC-2GD5Motherboard:
http://www.amazon.com/Gigabyte-1150-D-S ... -B85M-DS3HHDD:
http://www.amazon.com/WD-Blue-Desktop-H ... e+WD10EZEXRAM:
http://www.amazon.com/Crucial-Ballistix ... +DDR3+1600PSU:
http://www.amazon.com/EVGA-80PLUS-Certi ... s=550w+psuThis comes in at approximately $677. I know you said you had a credit of $650, but this build gets you some high quality parts. The only part I'm not crazy about is the motherboard. It is a barebones board that offers just enough for your needs. If I were to build a gaming PC that didn't have to be super high end, then I would buy all of these parts expect the board. I would try to scrounge up another $50 and buy a better quality board with some overclock features (since the 4670K has an unlocked multiplier and is made to support overclocking). With that said, you will still get great performance with the board I listed. The MoBo doesn't really add or remove much in terms of performance. Some chipsets are faster than others and support more or less USB and SATA ports, but that is about it.
I'm an Intel and Nvidia guy. I feel as though they offer the best performance and longevity. Without the need to upgrade as often to meet the needs of current software / games. Admittedly, AMD GPU's offer better performance for the money. However, I have personally had bad luck with AMD GPU's. I recently spent $800 on two R9-290's, got them in the mail, immediately installed them and literally got no picture on my monitor. I knew the PC was booting because I could hear the Windows welcome tune as well as POST beeps and such. After hours on the phone with XFX, the manufacturer of the cards and EVGA, the manufacturer of my MoBo, both concluded that the cards should work, but they don't. I returned them, bought two GTX 760s installed them and started gaming immediately. This is just my experience. I will probably revisit AMD again in the future when I upgrade two a new platform and see if I have better luck.
So, the reason I chose that specific GPU is because for approximately $150 you get a GPU that has a very low TDP, so it puts off very little heat and uses very little power. Also, this card is capable of running most modern games at 1080p with high setting, at frame rates well above 30, which is considered the minimum acceptable number.
The CPU I chose has shown over time that it will run games at the same benchmarks as higher-end i7 CPUs. Basically there is a point where CPU's stop affecting gaming performance and this CPU is the one that hits that point. Anything above this CPU's capabilities are meant for high level multi-tasking.
The RAM is fast, high density sticks from a big name in the PC industry. That's about it. Also, since you get 8GB from two sticks, you have room to expand later.
The PSU is a low wattage, but is a quality piece which I have used in the past. EVGA has excellent quality and customer service.
The HDD is standard fare. 1TB from Western Digital. Not an SSD, but your budget didn't really allow that for what I would consider priority. However, I would upgrade to an SSD sometime. You will see a gigantic jump in speed and performance.
The case is just a standard Mid-Tower case from Rosewill, which is a budget brand, but they actually make good quality products. This case has plenty of air flow and it's not too hard on the eyes.
The Motherboard is the only item I feel is a compromise. Like I mentioned above, if this were my build I would try to find a little extra money to buy a better unit. Gigabyte is a brand that is the top of mid-tier companies. They make nice products that are comparable to the higher end brands like EVGA and ASUS. This motherboard uses the B85 chipset that limits its available USB and SATA ports. As well as the number of PCI-e slots it can have. In this case it's one PCI-e 3.0 x16 ports and a second PCI-e 2.0 x4 port. This limits the usage to one GPU and a second low speed PCI-e device. The last limitation of this board would be the BIOS options for overclocking. This isn't important to some folks. Most people will never use those features. But since the CPU I listed is capable, if not made with overclocking in mind, then why not get a board that can support that capability? Again, I want to stress, that this board will be just fine for this build and will not hinder your ability to play games in any way.
This is just my idea of a good $650 build. It went slightly over, but I think the extra $25 or so would be completely worth it.