Fully Approved Sources:
Complete Arcane (Invocations Only)
Complete Mage (Invocations Only)
Expanded Psionics Handbook (Psionics Only)
Complete Psionic (Psionics Only)
Players Handbook II
Tome of Battle (Blade Magic)
If the book or spell you desire is not listed, it is most likely not approved yet but may still be requested to be added to the list.
None so far.