An i3 isn't as nice as an i5 but for gaming you're better off spending the money on the gpu. Starcraft is the only game where the cpu will bottleneck the gpu much, but it will still run perfectly since it's easy to run.
I'd have selected a 6950 but newegg seems to only have one left. The 560ti performs at the same level though.
Lot's of things can be upgraded but this build will let you play any current game on max.
If you want to spend more money do the following: (most important to least)
-upgrade to an i5-2500k
-cm 212+ cpu cooler (for a nice oc)
-better gpu (to future proof your build I guess)
An boot drive SSD would also be an awesome upgrade. It won't help games but it makes windows boot instantly and gives you a snappier windows experience. Many people would consider this a necessity.
Also there are lots of aesthetic changes that could be made, point to anything you don't like.