You could opt for a Phenom II X4 955 BE, save on some cash on relevant components and go all out for a HD 5850.. If you want to build up a SLI setup then getting the GTX 460 1GB is highly recommended..
With an i5 750 and a 460, you won't need SLI for excellent gaming at 1920x1080. For insurance against new games needing more, make sure your mobo has two PCIe x16 slots (even running at 16x-4x) and your psu is 600W or so. That way you can add a second 460 if and when you need it, without spending more than a few extra bucks now.
I'm sure a lot of people upgrade CPUs without changing the mobo. My personal experience is a bit different. When I buy a system that will last for three or four years, I find the whole world has changed by the time I need an upgrade. Your experience may vary.
I think it would be safe to say that buying a GPU right now would be a bad idea. I'm reading that there will be some price cuts soon that might knock a better GPU into my budget range. I suppose I won't settle for an underpowered 5770 or a non CF-able GTX 460.