I7 930 and radeon 5850 or i5 750 and 5870.

The i5 750 and the 5870 will give you better gaming performance now. However if you wish to go to crossfire the i7 930 would benefit more from that, although it won't be that much of a difference, so i'd say stick with the i5/5870

I thought that it might be better. the only thing that makes me hesitate, is that in the future if i want to upgrade the rig if i get a core i5, id prob have to buy a new motherboard and cpu to get a core i7. If i got the 930 and 5850 id just get another 5850 when the prices drops and crossfire it.

You make a valid point but it depends on how quickly you will be upgrading. If you're gonna upgrade in less than 2 years, I say buy the 930 and 5850. If you're gonna upgrade after 2 years, by then, much better processors/motherboards/gfx cards will be out. So you'll want to change your motherboard/cpu/gfx card anyway, so get the i5 750 and the 5870. I would personally go for the AMD AM3 platform since it will around for some time in the future, hopefully more than 2 years.

personally i would go with the 5850 and 930 if u think there is a chance ur going to crossfire. You can always crossfire a 5870 with the 5850 later. any of the 5800 series cards will crossfire with each other.

i5 750 and 5870 is the best option. That rig will last you a few years easily, more if overclocking. By then whether you bought i7 or i5 socket will be irrelevant as the new stuff will use neither.
As for XFire, just buy a decent P55 board, x8/x8 instead of x16/x16 is actually very little performance difference, you wont even need to XFire the 5870 for a long while and when you do the performance difference will be so small you wont even notice it.
The performance of an i5 750 and 5870 will be notably better than an i7 and 5850, and that will be a bigger difference than the difference between 2 x 5870 x16/x16 than 2 x 5870 x 8/x8, so worth getting the i5. Also, if you spend more on CPU and get the lesser card when you XFire you will go with 2x 5850, whereas if you get the i5 750 your second card will be another one. 2x 5870 x8/x8 will run better than 2 x 5850 x16/x16

You also have to consider the performance difference that will come from 6gb of triple channel RAM with the i7 compared to the probable 4gb of dual channel RAM you would get with the i5. It probably wont be that noticeable in average daily use, but it could matter if you're going to be using memory intensive programs.