I tend more toward the "budget box now, screaming box later" method.
To that end, if you want to conserve some cash, you might consider going with a single 5870 card and then worry about getting a second one later (if you even need it). Just make sure it has at least 1GB video RAM on board. Take the money you would've spent on that second 5870 card and invest it or something. By the time you need to buy a second one, you'll have earned some interest and the price of another card will have come down enough to match whatever your savings would be through work.
Another thing to consider might be to go instead with the i7 860, which has
the best price/performance ratio of any current CPU. It's priced about the same as the i7 920 but has clock speeds and performance similar to the i7 940. Yes, the memory is a little bit slower than the i7 since it is only dual channel (about 8 percent slower
according to one test), but you probably won't notice the difference while gaming since it can actually turbo up faster than the 940. And you'll save a little money by only having to by 2 sticks of RAM instead of 3.
I agree that one DVD drive will be enough. Like my video argument above, you'll probably want to get a second one later, but you'll want it to be Blu-Ray or something, and it's going to take some time for the prices to come down on those.
Unless you plan on loading up on media, a 1TB drive should be sufficient for gaming (unless you like to keep all your games on your HDD for ever and ever and ever).
Sound is pretty much a given. Most mobos come with Realtek sound that's good enough (5.1) for pretty much anything you could need, unless you plan to use it to power a home theater system. Even then, built-in sound would be 'good enough.'
A good 1156 mobo to consider might be the
GA-P55A-UD4P, though if you want to get totally ridiculous, you could blow all the money you've been saving on the other parts and go for the
GA-P55A-UD7. Actually, that doesn't sound like that bad of an idea, if the board actually lives up to its specs. Ten years from now, either board might not be up to gaming any more, but they'd still make a great router or server or something.
--Patrick