The Fochlucan Lyrist from Complete adventurer, full BAD and full progression in both arcane AND divine spells, multiclassing is a prereq.
Geomancer from Complete Divine. 3/4 BAB, full caster progression. multiclassing is a prereq.
Eldrich Thurge from Complete Mage. 3/4 BAB, 10/10 invocations, plus 10/10 arcane casting. multiclassing is a prereq.
Lyric Thruraturge from Complete Mage, if your arcane caster is a bard. 3/4 BAB and full bardic casting progression.
*Slight modification* Stormlord from Complete Divine. 3/4 BAB, full caster progression. *NOTE* this is for divine casters only, however I've never understood why. It'd be some houserule modification requiring DM approval, but I think this would fit for an arcane caster easy.