@acer 

I suppose it will be different for each person but the ones I would put at the top of my wish list would be the same kind of coverage of wavelets (though for signal processing reasons not image processing)

http://www.wolfram.com/mathematica/new-in-8/wavelet-analysis/

And the ability for Int to get the right answer on oscillatory integrals

http://www.wolfram.com/mathematica/new-in-8/new-and-improved-core-algorithms/solve-a-numerical-integration-challenge-problem.html

I can do without the graphs and groups finance or control. And texture mapping and wolfram alpha stuff go in  "cool, but not needed".