In order of importance for gaming builds:
1. Graphics card - This is what matters the most.
2. PSU - Depends on what type of graphics card you get. 500W's is a good minimum, but you can find good 650W PSU's for $10 - $15 more.
3. CPU + MB - Not entirely important, but cost per performance means a SB CPU or an AMD APU.
4. Case - Good airflow will help lower the heat build-up of your CPU and Graphics card.
5. Memory - No need to have more than 4GB's memory.
6. Storage - Games will install, uninstall, and load faster with a SSD, but HDD's give you more GB/$.
El I am gonna have to disagree with some of what you have put here. The determination of CPU or GPU is really dependent on the type of game to be played. RPGs, MMOs and RTS games all benefit more from a CPU than FPS games do. These are also the games most likely to push multi-cores more in the future and the most modded thus often needing more RAM than other games.
Now I will not disagree about getting the best video card you can afford but the CPU does play a factor.
As for which CPU, right now it is hard to suggest an AMD based system. Intels i3 can run right with the Phenom II and the FX 4100 and as you get close to $200 the i5 holds a solid lead over anything AMD has.
In the case of the PSU you are dead on the mark, DO NOT SKIMP on the PSU, a cheap one will make a great system run like crap! Possibly even damage it.
However I also suggest not skimping on the case if the budget allows it. A good case can last you for years through a number of builds.
RAM, unless your budget is really tight get 8 gig. Yeah you may not need it now but the price is excellent and it never hurts to have more than you need. The $20 savings of a 4 gig kit over an 8 gig kit is not worth missing out on the extra RAM unless it is going to break the budget.
As for Storage again it depends. If you can break the PC hoarding habit and will be running a gaming system with just one or two games at a time, then the SSD is the way to go. A 60 gig SSD can hold a couple of games, the OS and some other programs pretty well. However if you are a packrat of software and data then it will be to small. 120 Gig prices have fallen to around $130 making them very attractive but again you need to be a disciplined user. However the reward for that discipline is a system that is much snapper and offers a quicker computing experience.