Tears to Tiara, Guin Saga Recommendations
Both are epic fantasy anime from spring season 09. Both are about siblings fighting a war they didn't start. Both pair of siblings have royal blood in their veins, and are aided by a magical creature (Guin/Lord Arawn). Both female leads are some kind of prophets and sorceresses.
Tears to Tiara contains a few fragments of comedy, which makes it slightly less dramatic than Guin Saga. But both anime are great entertainment and if you enjoy one of them, then you should be able to enjoy both.
They are similar because both are about siblings that go to war with a more powerful force, but it's mostly because you get the same kind of atmosphere from both of these shows