i7 2600k (overclockable) - 4 core / 8 thread $369.99 - $90 instant in-store savings = $279.99
i7 2600 4 core / 8 thread $329.99 - $80 instant in-store savings = $249.99
i5 2500k (overclockable) - 4 core / 4 thread $249.99 - $70 instant in-store savings = $179.99 (Tom's Hardware 2011 Recommended Buy)
i5 2400 4 core / 4 thread $219.99 - $70 instant in-store savings = $149.99
These are all socket 1155 - you will need a new motherboard for these chips!
These are "mainstream" not "enthusiast" chips. From what I've gathered, its not much of an upgrade if you already have socket 1366 - more of a sidegrade. For everyone else, looks to be a big upgrade. That being said - look at the reviews above and see the i7 950 being outperformed in a bunch of tests. In fact, the 2600k is being compared to the 980x by some.
Enthusiast chips from Ivy Bridge should be released early 2012.
If you want to use more than 2 GPUs, you need a motherboard with an NF200 chip, which increases latency.
Edit: Added PDF file (thanks RANDALSW) as MC took down the advert