hmm... Usually mods come with new maps, but they require the mod to be funning to play them.
I would reccomend Dirty Sanchezze's Map Pack
This is the home of Sinperium's Spellbound map. It's hard, but you might want it anyway.
There is also another map of Sinperium's, Wolfpack! Sinperium makes cool maps.
Yes, there is a website with maps. It's called WinCustomize (Link is to the maps page). It requires an account to download antything, but when you register an account on here, an account is automatically created on the Demigod website for you, the Stardock website, the Galactic Civilizations website, and pretty much any site associated with (and owned) by Stardock, including WinCustomize.