modern companion readings to 'tiberius caesar'

As Lindsay Powell pointed out on our Facebook group page, there are excellent and more modern biographies of Tiberius out there after G.P. Baker, our current read:

Tiberius by Robin Seager and Tiberius the Politician by Barbara Levick. The latter is also a good source for Augustus.

As to novels, aside from Graves' I, Claudius there is Tiberius by Allan Massie.