Nice rig, if anything, you won't have to upgrade for a while. The graphics you have is one of the best single gpu's out there. I'd have to say when graphics companies get their act together and make something that can play games properly, that's when you should upgrade. Although an upgrade here and there for the graphics wouldn't hurt, except maybe your pocket book.
You seem to know how to build a rig. Was using only 1 gig modules in two slots an accident or a knowledgable research choice? Cause not many people would choose such a setup.
I've been studying computers on my own time cuz I still go to school, and for this build all the parts I chose were based on my needs, and then on price to quality ratio, and compatibility. For each one I had to read dozens reviews and articles until I decided to choose what I did. 2x1GB in dual channel is always better than Single Channel, and it was in fact a knowledgable research choice.
In other words: other ppl are noobs
An excelent example: AMD Phenom II 550 BE. 100$ for a cpu that is capable of quad core (for when games start taking advantage of it more), and excellent overclockability with the help of an aftermarker cooler, and you got yourself an excellent cpu for a very long time.
PS: this is my first build which I made for 3 hours perfectly. Excelet airflow and cable management, fired it up from the first try.