I can highly recommend this book for lots of good info with an emphasis on photography:
http://www.amazon.com/Photographers-...e=UTF8&s=books
I second the hike to Vernal and Nevada falls. Tip, on the way back down take the John Muir trail instead of the Mist trail and not only is it less steep but you'll get some alternate views of Vernal Falls.
Make the drive up to Glacier Point if it's not already closed (they have snow up there yet?)
Check out the Mariposa Grove
And of course you'll want to hit the scenic turnouts in the valley: Tunnel View, Valley View, Sentinal Bridge, etc.
If you're not going to be there very long I'd focus mostly on the Valley and nearby locations, as you'll get the most photographic bang for your buck/time.