Hey Joe a Cheem.
I just built a new system, and posted some questions here as well. I did a lot of research on tom's hardware, and overclockers dot net/com, and there is a TON of information and opinions out there.
For 1500$ this is my opinion on how you should begin to proceed.
First, Toilet Duck(TD/Till Death) had a great reputation here. The pictures I've seen of his builds show a clean and professional job done in terms of the cabling etc. He has very strong opinions on what the best components/manufacturers are, and for the most part he has selected the best stuff for his systems. As Spikes said however, building a system isn't rocket science, and with the help of a few uTube videos and "show me how" websites, you can likely figure it out and built a system from purchased components in part of an afternoon, not counting the operating system install, drivers, tweaking and such. I was going to get TD to build my 2500$ system 18 months ago, but when I emailed him he responded that due to me being in Canada, I should just "look locally". Considering the pain that customs can be, I don't blame him. He was also just coming off the big "battle" thread where he decided to take his leave from the boards here. His first response to my inquiries was "I'm not giving any more discounts to Aces High players", which was interesting, since I hadn't asked for one, only information regarding what type of system he could build me for my budget. As I said, he has a very solid rep in both building and customer service, and you won't go wrong if you get him to build your box for you, but again, it isn't brain surgery and you CAN do it yourself. That's what I ended up doing, and don' regret it.
Now, on to the components. This is all my OPINION, which is based on others opinions that I've read through researching the above forums and sites.
1. Processor and Motherboard. Right now it boils down to deciding if you want to go with the most current 2011/x79 motherboard/cpu, or the still current but more dated 1155 setups.
1 a:The 1155 gives you several great CPU's to choose from, the i5-3570k, the i5-2500k, the i7-2600k, and the i7-3770k. The 3570k is the cheapest at around 200$ish , with the 2600k and 3770k being around 300$ and change. The motherboards will range from 130$ish for a basic entry level to around 200$ for the "best bang for buck" type such as the Gigabyte UD5 or ASUS P8* series somewhere in the middle. The i5 3570k with the UD5 board can be found in package deals for sub 400$, and if you choose to go the 1155 route, this is the best value for the dollar IMO, as the 3570k will overclock safely and easily to the mid 4 ghz range. Since you said this is primarily a system for gaming, the 3570k will perform within a few percent of the 3770k's numbers, and cost you probably more than 100$ less, money that you can invest into the GPU/vid card. So unless you plan on doing a lot of video editing or similar work, the 1155 solution is the i5-3570k most likely.
1b: The other route is to go with the newer 2011/x79 setup. Yes, it is a lot more money. Yes, it barely outperforms the 3570k, 2600k, etc, and in some cases is even SLOWER than these 1155 CPU/Chipsets. That said, there is a whole bunch of new CPU's for the 2011 just over the horizon, and if you go this route now, you'll be well situated to take advantage of these new CPU's as they are as reported so far going to plunk right into the 2011 mother boards. So, in 6 months time, you would be able to sell off your i7 3820 chip and replace it with whatever new fangled CPU suits your fancy. The i7 3820 CPU is around 300$ish, but the mother boards are a fair bit more expensive. The Saber Tooth from Asus is in the mid to high 300$ range, and the top of the food chain RIVE is close to 400$. If you go this route as I did, the CPU/MB will cost you close to 700$ instead of somewhere under 400$. For your budget, I just don't see it as viable, but I thought I'd throw this out there to give you an idea of the current playing field.
2. GPU/Vid Card. This is likely the most important component when it comes to gaming. There are obviously two options, either NVidia or AMD/Radeon. You can't go wrong with either, and you will get a lot of opinions on where the "sweet spot" of performance to price ratio lies, but Toilet Duck has it right with the selection of the 7950 Radeon. A lot of guys will say the 6870 is the way to go, and they really aren't wrong, and it's a close call here no matter what route you travel. Also, that 100$ I talked about that you save with the i5 CPU can be put to use here, and you can jump up a bit to the Nvidia GTX 670 or 680 cards. The 670 is the "sweet spot" according to many for the Nvidia cards, and you can find a basic 2gig one for 350$ like the eVGA 670 FTW LE, or one of about a dozen other brands/types. Also, if you want to spend about 150$ more than the 7950 card, you can bump up a little more to the GTX 680 for about 450$ish. One thing to consider is that the 7950 will overclock like it was built for it, with a program like Afterburner, you can simply O/C this little gem to 7970 performance levels. Many guys on the "in the know" forums say that getting a 7970 is almost pointless since the 7950 o/c's and performs so well, and it was my 2nd choice in a close call for my GPU until a sweet deal for a gtx690 fell into my lap. Anyway, IMO the 7950 is the best option for a 1500$ system.
3. Case. This is a subject of a lot of debate, and you can easily get by with a 100$ case Joecheem, but make sure it is USB 3.0 compatible or you will kick yourself later, especially if you use a thumb drive to transfer stuff around, or a million other uses for it. I was going to go with the Cooler Master CM 690 II advanced with the USB 3.0 support, and it was around 100 bucks, but I decided to go up a little to the Corsair 650D, which is a case with better construction. That said, considering your budget, I would go with the CM690 or something very similar in options and price. Remember you will likely be overclocking your little wonder CPU the 3570k, so you'll want some extra fans. The Noctua 140mm twin fans fit right in that case, and will help to shore up the cooling in this case, which is already pretty good with the stock fans. The Noctua NF-P14 FLX 140mm Fans can also replace the fans on the CPU cooler that I'll suggest next.
4. CPU Heatsink. Considering you should overclock the CPU as mentioned in order to get the full performance from it, you'll need a good heatsink/cooling solution. For air power, the Hyper 212 EVO CPU Cooler from Cooler Master seems to get a lot of positive feedback and recommendations, and it's around 30 bucks or so. That said, I really think that the Corsair Hydro H100 Extreme Performance Liquid CPU Cooler is the way to go. Yes, it's 100$, triple the cost of the best air cooler, but it's REALLY worth it for that little i5 chip, it is all the rage with most builders. TD uses it in a lot of his builds I see as well. They are virtually maintenance free, work fantastically well, and really let your o/c the snot out of your little i5 CPU.