Intel will begin releasing the Haswell Refresh CPU's in Q2 2014 according to data shown to VR-Zone. Included in the lineup is the Core i7-4790, 4690, 4660 and i5-4590 as well as two lower TDP forms with a T and a low voltage S model. These will be compatible with existing components that supports the 8 and 9 series chipset. You can see what the plans are in the roadmap below.
Image courtesy of VR-Zone
The i7-4790 will replace the current i7-4770 and will increase the default clock speed by 100Mhz bringing it to 3.6Ghz. You can see the rest of the details below.
So other than the increase in default clock speed there really isn't much difference between the Refresh models and the original Haswell's.
Stay tuned for more information on pricing and availability as we get closer to release.