Black Friday/Cyber Monday. Basically certain parts will be on sale at different times throughout the year. But Black Friday/Cyber Monday and the week or so after Christmas are the best time to find overall price drops.
I doubt DDR3 will get much cheaper. At least until it is replaced.
Generally ~Feb/March during the slow season there will be some general price drops, but this year with so many new releases coming out at that time I doubt there will be many deals to be had (except on old hardware). Perhaps 4th of July?
The simple fact is that high end hardware does not go on sale, and when it does it is only $10-20, which is not enough to make waiting worth it if you already have the money saved. Only expect good deals on mid-low end hardware.