Vecna and his worlds-dominating plans has become a central figure in our 8-year campaign. If I allow a meeting, I want to be ready with an awesome, God-like immortal with multiple prestige classes, Divine Rank and world-shaking POWER.
Vecna is statted up in Deities and Demigods page 94 as a Cleric 20/Wizard 20 with 10 divine ranks. He commands 9th level arcane and divine spells, as well as 12 salient divine abilities, which is pretty earth-shaking.
You can find the update document that corrects the 3.0 book to be 3.5 compliant here.