On ground exchange---possible but costly and less appetizing when things go wrong.  I have several friends that have invested in such systems and their dissatisfaction comes from when things go wrong underground.  

Only portions of the US have areas where wind is "reliable."  It should be included in this mix, but you can't just turn the wind on.  And as was demonstrated in CA this past summer and previously, heat waves tend to correspond with low wind just when you have the highest demand.  CA's problems were also compounded by the NG compressor cooling issue.

As for solar, I think we are probably far enough along on higher efficiency PV cells that we should consider jumping forward with them.  Solar thermal also has some promise in certain areas (e.g., Kramer Station in CA).  A point worth considering about solar cells is that the higher efficiency cells require substantial initial energy input as well as fossil fuels.  If we wait to long, solar will look like an alternative we wished we had taken and would then be tantilizingly "out of reach."