Next thing to upgrade for gaming

I would get the 560ti. Worry about the cpu later, they're cheap and there won't be a big enough bottle neck to worry about   Also, if you get the 560ti and don't buy a new psu you can get a new CPU. At 500w you could easily run the 560ti safely. In fact the 560ti recommended PSU is 500w. You're safe! I'd pick upt he 560 and buy a new CPU   (ignore the psu it's fine, as well as your ram)

The real question is: IS it brand psu or a generic one.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

is that good enough for 560 ti for now and maybe and i5 down the road?

Easily!   Your'e golden, just like your PSU. So simply, keep PSU, get new Video card, then new CPU. I'm sure you could get any CPU on the market and you'd be fine with the 500w. The recommended wattage for the 560 is 500w, but that INCLUDES the average wattage a PC will use (cpu, ram, harddrive, diskdrive). Anyway, good luck!  

PSU is fine for the 560

But you will need a new mobo for an i5...

I think you have a relatively well balanced system.
It is not clear to me if you would benefit more with a gpu upgrade or a cpu upgrade.
Usually, a gpu is the most effective for gaming.
To help clarify your options, run these two tests:

1) Run your games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.

2) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 70%.
If your FPS drops significantly, it is an indicator that your cpu is the limiting factor, and a cpu upgrade is in order.

It is possible that both tests are positive, indicating that you have a well balanced system, and both cpu and gpu need to be upgraded to get better gaming FPS.The psu requirements are almost entirely gated by the graphics card.

The GTX560ti will run on a 500w psu with 30a on the 12v rails.
Your psu is an older one which does not specify the maximum 12v amps. It would likely work since the requirements tend to be conservative.
I would certainly try it first unless you have some suspicions that your psu is a problem.

If you go the cpu route, you will spend about $ 450 for a 2500K, P67 mobo, and 8gb of ddr3 ram.
Less what you can market your E6500 and ddr2 for. The mobo will not sell.

I would replace everything, especially if your gonna play shogun 2...I play Shogun 2 with a i5 2500k,4gigs of ram and a gtx 295 gpu and it can struggle at times at max settings..I play at 1920x1080..I'll upgrade my graphics card when they release a new Nvidia Card or AMD card...Just save your money like i did and build yourself a new system...

well, my budget is limited and i dont really aim to max all the games i play. I just need it to be high enough to enjoy the eye candy and have decent frame-rate. I will replace everything by the end of the year but for the time being, i can only either upgrade CPU or GPU

Well a gpu uprade from a 9800 to a 560 will be considerably more beneficial gaming wise than a cpu upgrade, regardless of the bottleneck your cpu may give the 560 ti. So if you have to choose one, get a new GPU. But considering the price of a 560ti, you'll have more than enough to get a very good CPU