The Core i7 3687U is currently the market leader followed by Core i5 3437U processors and both of them cost most than what we would like to pay for them. Core i7 3687U officially sells for $356 while Core i5 3437U sets you back a bit more modest $225. Both of them are based on Ivy Bridge dual core and have 17W TDP.
In Q3 2013 Intel plans to introduce at least two new U series processors branded as Core i7 4000 parts. At least some of them will feature a 15W TDP. There is no mention of the new brands, but Core i7 and Core i5 are expected to show up with 15W TDP, or 2 W better than the previous generation.
Haswell U series also comes with a 25W TDP, a more standard voltage, but traditionally these 25W TDP parts don’t cost as much as 15W or 17W TDP ultra low voltage parts. We expect to see some slightly faster processors than Core i7 3687U based on Haswell U series that will perform better at 15W, as of Q3 2013.