I agree with Ketone and Synfrag here, they have very valid points. I would steer well away from ready-made builds, as most of them are completely terrible and inbalanced (they sell on big numbers, say proper Intel i5 processor, 16GB RAM, 500GB hard drive and then you get Geforce gt540 as graphics card. Not gonna play much on that before you get new graphics). Having someone experienced build one for you is a lot better choice, he should know about bottlenecks and cooling and power supplies. Point about custom computers requiring more maintenance is not very true either, all computers require some maintenance, and if pc is built well, no more maintenance should be required when compared to ready-made.

As for the parts. They look very good in general, but you could still get a faster graphics card and not have other system hinder it. If it fits to your budget, consider 560 or 560ti or even something from 600 series instead of the 550ti, I'm running overclocked 560ti with i7 930 (2.8 GHz quad core, should be a bit slower than that i5 if I remember correct) and cpu is nowhere near full utilisation.

Amount of memory is good, but I would also suggest going for a better brand, those Synfrag said and Kingston are very good.

Importance of a good quality power supply cannot be expressed enough. Get a good quality PSU, pay a bit extra for that if you have to. When power supply fails, it can and will take other parts with it too, and that's no fun. Corsair, Seasonic, Antec, Cooler Master come to mind as brands that are known for quality. For your system, I would get ~600W supply, 500 might make it and 700 is just too much with just single graphics card.

SSD drive can make your computer run faster (significantly) but will take the price up too. You will need normal hard drive with or without as SSDs have limited space, they're fast but small, large enough to have operating system and some software on them, rest will have to be stored to the normal hard drive.

Intel i7 930
6GB Corsair Dominator @1600MHz
MSI GTX560Ti Hawk
Samsung F3 1TB
Antec 300
Cooler Master GX650W