Our friends at Beamdog are running an excellent sale on Disciples II: Gallean's Return, which is a compilation pack of both the original Disciples II: Dark Prophesy and its standalone Guardians of the Light expansion pack. For the rest of the weekend, you can pick it up for only $3.75.
Or, if you'd like to jump directly into the latest entry in the series, Disciples III: Renaissance is currently on sale for $14.99.