Built my current system about 2 years ago:
Case: Fractal Design Node 304
Mainboard: ASRock Z87E-ITX
CPU: Intel Core i5 4670K
Memory: Kingston KHX1600C10D3B1K2/16G
GPU: MSI Radeon HD 7850
Disks: Mushkin MKNSSDAT240GB Atlas mSATA 240GB SSD +3TB HD + 1TB HD + 500GB HD (I also have another 2TB sitting in a box).
Optical: ASUS SDRW-08D2S-U
OS: Microsoft Windows 7 Home Premium Edition 64Bit
Monitor: ASUS VS238H-P 23IN
CPU Cooler: Corsair Cooling Hydro Series H90
PSU: Silverstone Strider ST60F-PS
Can be interesting trying to stuff everything in to a small ITX case. Got additional short PSU cables to help, but it is still pretty tight. Shortly afterwards I had some buyers remorse in not getting the i7 for an extra 100$, but really I've had no issues with the i5 so it is probably moot. I decided to get 16GB of RAM, which is a bit of overkill really, however I was more influenced by the fact that the MB only had two slots and its in an ITX case, so if I ever wanted to go beyond 8GB, it would be a super PITA to change out, it was inexpensive so what the hell right? Went with a pretty modest graphics card as the price was right, had to be careful of actual dimensions as not all would actually fit, so far pretty happy. It is primarily a gaming machine, and so far it hasn't balked at anything I've thrown at it, though that said I play DOTA2 99% of the time, which isn't all that demanding anyway. The SSD is kind of neat as it is a MSATA, which plugs into the back of the MB. On the plus side, the case includes 3 HD hangers to fit 6 drives (which are pretty cool btw), however the video card effectively reduces that number to 2HD hangers to fit 4 drives, but the SSD doesn't take up any of that space. On the negative side, it is on the back of the MB, in a tightly packed ITX case, with no removable back plate, which means it is effectively there forever, as I don't see myself ever totally dissembling everything to get at it again. The optical was a good decision also. It is external. I use it rarely. I plug it in when I need to, and when I don't it sits in my desk out of the way. Win7 as didn't want to deal with Win8 at the time. Got the cooler for giggles mostly, it's the biggest you can possibly fit in the case, so that is kind of fun.... PSU had several nice features, size being one of them being important in an ITX case (it is smaller), its HE yet still a decent amount of headroom in total wattage, and it also was modular and had optional short cables, also important in an ITX case. So far I have 3 of 4 hard dives installed. I had a 2TB fail on me, replaced it when a 3TB, then had the warrently go through and got a free 2TB, however I still have plenty of space so I have never bothered to hook up the new 2TB into the system. Once the 3TB media drive starts getting too full, I'll probably throw it in there, as there is just room enough. Anyway I am pretty happy with my system. It is a gaming system, but an intermediate one. Another important purchase I made afterwards was a silent mouse, making girlfriend compatible gaming much more enjoyable! :)