Your monitor (Samsung SyncMaster 906BW from the other thread) runs a max resolution of 1440 x 900 so unless you plan on changing it for a larger monitor which supports higher reoslution you can look at lower specification graphics cards and check their performance in reviews/Tomshardware/Anantech sites to see if it would be suitable for your gaming needs. I suggest looking at benchmarks and search for the graphics card you are considering and the games you play to see how it performs at the 1440x900 (or similar 1680 x 1050, 1366 x 768m etc.) resolution.
Just one, 4GB should be fine. Plus you can always get more later if you need it. For gaming anything over 8GB is generally considered overkill. I'd start with the 4GB.
Processor:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115220 This is the most expensive item, should i stick with the i5, or can i go with an i3?
If I remember correctly i5 is a quad core (4 CPU cores in one) part. i3 is dual core, with this is in mind more and more games are utilizing multiple processor cores so I wouldn't recommend anything below a 4 core processor. If you want to save some money I'd go for an AMD quad core or 6 core CPU instead of the i3. You won't need the i5 for the games you have listed but it is a better performer. What you are looking at is from the first generation of Intel i processors (socket 1156). I would look at the i5 2400 (socket 1155) instead. ~$15 more for on average 20% better performance, but we can possibly make savings on your other choices.
For a cheaper option either and AMD Phenom II processor (X4 or X6, 4 or 6 core), or one of the new A8 ones with the Fusion core.
Phenom II X4 could be had for about ~$50 less than the i5 ($129.99) and a AM3+ motherboard for under $100 and give similar gaming performance in most current titles. And AMD will be releasing a new processor range(Bulldozer) that will use the same AM3+ socket so gives you room for upgrades in the future.
With the AMD A8 option (
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103942 - $139.99) you could do what we discussed in the other thread and get that system without a graphics card and use the built in GPU, and get a graphics card later on if you felt you needed it. Only thing is I haven't really been that interested in the Fusion APU(combined CPU and GPU) series from AMD and have no knowledge of their roadmap for upgrades for the FM1 socket motherboards it is paired with.
Motherboard:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131783 nothing much to say about it, does it work with everything else?
You have picked out a socket 1155 motherboard so your original CPU choice (socket 1156) wouldn't have been compatible. It's a different version of the one I have in my computer (Asus P8P67 Pro). A good choice. Although you can get cheaper motherboards the Asus is a good choice in my opinion. I'd maybe look at the Z68 chipset motherboards. This is a newer intel chipset and allows for the use of the graphics core that comes on the i5 processor. I believe most motherboard manufacturers are producing boards with "graphics switching" that allows the use of the low power GPU core when just doing stuff in Windows/OS and the dedicated graphics card when gaming. This saves a little on your electricity bill and means you don't have to listen to graphcis cards fan spinning when your on facebook/email etc. It's not going to be good enough for gaming but it also gives you a relatively free backup in case anything goes wrong with your graphics card,
Perhaps -
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128520 $99.99
Or -
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128502 (with USB 3.0 if you think you'll need to use fast external hard drives or other devices) - $113.99
http://rethinkthought.com/intel-sandy-bridges-h67-p67-and-z68-differences-explained/
I have no affinity to Gigabyte. Just they are the most recognized and liked brand with a low price for a Z68 based motherboard. This lets you use the i5 graphics core if needed (same as H67) and like the P67 chipset it allows for overclocking. The i5 2400 processor itself doesn't allow for overclocking but if you can have the feature available for maybe an upgrade to a faster processor (i5 2500K, i7 2600K or future overclockable K processors) in the future for the same price as a similar featured H67 motherboard then you might as well have it, no?
Yes, but there are cheaper and just as good options -
http://www.newegg.com/Product/Product.aspx?Item=N82E16811815006 $24.99 special deal
or at a similar price you could get
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119161 or
http://www.newegg.com/Product/Product.aspx?Item=N82E16811163168
Generally in cases the names to look for are Coolermaster, Antec, Silverstone, Lian-Li, Thermaltake and some others. I've never heard of Sentey so would be inclined to go with one of the bigger names.
video card:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814141117 How is this card, will it work with my other items?
It will work. The current generation of AMD graphics cards are the 6*** series. I'd opt for
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150542 for the same price as the card you selected plus it comes with a voucher for a free game!
Fine choice. I've personally favored Samsung Spinpoint disks for sometime. The WD one is listed as SATA 6GB. Only really Solid State Drives (SSD, uses memory chips instead of magnetic disk platters) really take advantage of this, a standard mechanical disk won't benefit from it (I'm sure someone will correct me if I'm wrong). Plus SATA 6GB connections on the motherboard are backwards compatible and will allow SATA 3GB devices to work through them. I'd personally go for a
http://www.newegg.com/Product/Product.aspx?Item=N82E16822152185 - $59.99, $20 saving.
Optical Drive:
http://www.newegg.com/Product/Product.aspx?Item=N82E16827106274 only thing i need this for is DL windows and maybe some games (age of mythology)
There are two internal device connection standards. Old one is IDE, current is SATA. For this reason get the SATA version -
http://www.newegg.com/Product/Product.aspx?Item=N82E16827106276. I would suggest using the CD/DVD drive from your old PCs but it seems that a SATA to IDE adapter will cost almost as much as a new cheap SATA optical drive...
Antec, good choice. I think that should be enough wattage as the graphics card selected isn't a high power consumption model.
Post what your total is for all the components. Others might be able to suggest builds for the same money that you might prefer.