Here is a quick comparison of the 3 levels of the new Core series:

http://ark.intel.com/Compare.aspx?ids=46472,43546,37147,

As you can see the i7 is the only quad core processor. The i3/i5 have integrated graphics.

If you want to upgrade to future multi-core processors your only bet will be to go with the 1366 socket as that will be the socket for enthusiasts. That's not to say the i3/i5 are not worthy of your choice. You get great power and a great price with the added flexibility of integrated graphics (not the best mind you.)