Livy, Seneca, Cicero, Virgil also featured in my Latin classes. I'm not sure of the relative difficulty levels anymore, though. All of these were fascinating for different reasons: Livy for the narrative, Seneca for the wisdom (see also Montaigne who heavily quotes Seneca in his essays), Cicero for his personal involvement in Caesarian politics and Virgil for his role as Augustus' propagandist and continuation of the Homeric tradition.

I should read more of these texts, I remember being really fond of Latin classes.

Edit: to concur with GP, Caesar's writings (de bello Gallico) were somewhere in the first half of the curriculum and were definitely regarded as relatively easy.