I'll take a stab at all I can bring to mind (and I'm sure I'm missing some):
1. Alexander Palace
2. English Palace
3. New Palace
3. Catherine Palace
4. Winter Palace
5. Ropsha
5. Grand Kremlin Palace
6. Palace of Facets
7. Anichkov Palace
8. Spala
9. Yelagin Palace
10. Kozumensky (sp?) Palace
11. Grand Palace at Peterhof
12. Gatchina
13. Chesme
14. Livadia
15. Small Palace in Moscow (not sure of its formal name)
Then there were a host of smaller residences in the main palace parks: Marly, the Chinese Pavilion, Peter the Great's Summer Palace, etc.
And a host of other palaces which were built for rulers, or their family members, or favorites and subsequently passed in and out of the tsars' hands: Pavlovsk, the Michailolvsky Palace, the Engineer's Palace, the Tauride Palace, the Marble Palace, etc.
In fact, I'm not even sure how what definitional parameters to wrap around my original question.
Maybe the simplest way is to ask what palaces did Nicholas and Alexandra have at their disposal for personal living quarters, should they have chosen, at the time of the revolution.
Additions or deletions, anyone?