Shadow/highlight adjustment for correcting contrast problems.
Healing brush.
A series of photographic filter effects such as warming, cooling, etc.
A curves adjustment layer that can be modified.
Ability to work with channels.
16-bit editing capabilities.
RAW support.
Additional adjustment layer types.
Ability to create actions natively.
ImageReady is included with Photoshop. It is a program designed primarily for working with images for the Web. I have never used it in the three versions of Photoshop that I have used. But it is there for those who know how to use it and who need it. There are a host of other features that I cannot readily think a lot of at the moment. I really like Photoshop CS, but since it appears that there is going to be a new version of Photoshop Elements soon, I wonder if it wouldn't be wise to wait and see what it has to offer unless you feel you really have a need for some of the features.
I use Photoshop Elements at work, and Photoshop CS at home. Although I find the additional tools in Photoshop to be very powerful and in some cases real Time savers, I find that I can still get very good results with Photoshop Elements.