DDR3 memory upgrade

Im currently running 3x1gb corsair dominator with Vista 64 and, considering the recent price drops, looking to add to that whilst being able to achieve a 4ghz overclock.

I've seen that adding another 3x1gb of identical ram would be pretty pricey so what would be the best path to getting 6gb of decent ddr3 from where I am? (Bearing in mind also i may end up wanting to add to it further to go to 12gb in future)

cheers

12gb is pointless :P
I would say either get another identical kit or go for a 6gb kit.

Get a 6GB kit and sell the 3GB kit on Ebay, that way you will get some of your outlay back :D