OK, theres a lot of stuff being suggested in here, and being a new PC builder, here are my suggestions.
Get this PSU. Modular is way better. This means that any cables you don't need can be removed. Otherwise you have a ton of cables laying around.
Edit: PSU capable of running SLI 570s.
SSDs are great. They increase load times and boot times, but do nothing for increasing FPS. You would need a second hard drive for storage, and theres some config to be done. If you dont feel comfortable with that, get a Western Digital Black drive and save from the Velociraptor. You can always get an SSD later after you have had time to research it more, and you'll have the black drive as a secondary. Don't worry about raid or any of that stuff.
If you only plan to game, get the 2500K. If you plan to do any video encoding or other stuff that utilizes multiple threads, get the 2600K.
As for video cards, just get one. I would go with a 570. 580s are nice, but over 200 dollars more. You can always SLI them later if you want. However, if you may do that, I would plan ahead and make sure to get a motherboard that support dual PCI-e slots at 8X. Make sure its not one at 16x and the other at 4x. Also, you may want to get a PSU thats 750 or 850. I don't know for certain whats overkill for a PSU when doing SLI, but I have an 850 with 2 cards and its great. I'd rather have too much than skimp out to save a few bucks.
Remember, you said you want to build a good gaming computer, not an amazing top of the line money pit. Whatever you build, there will always be something thats better that you didnt do. Decide whats best for you, and don't waste money on ideas that sound great. I've been in your shoes