There are a few economic powerhouse civs, and a few civs that don't quite measure up to that but are still very fun builder civs.
Ljosalfar are probably the archetypal builder civ. They're nearly impossible to invade, and they get big powerful cities. Svartalfar are similar but a lot more offensively focused. If you're going for a pure builder game, stick with the Ljos. Game highlights include aggressively terraforming the land and growing cities of incredible size. A size 35 city is well within reason for the elves.
Hanah Lanun are the kings of economic dominance in any map with high water. For pure commerce output they are very hard to beat. Game highlights include maximising use of coastal spaces, both for their inherent output as well as for pirate coves. As well the Lanun will be in a great position to do some heavy overseas colonization.
Khazad under Kandros Fir are another incredible builder economy. Their production can't be beat, and their use of aristograrian with financial gives them an insane level of food and commerce as well. Game highlights include managing gold reserves to control founding new cities, and then reaping the benefit of the best production in the game.
Those three civilizations are the kings of the builders. An honourable mention goes to:
The Kuriotates. A big part of the builder game is building the greatest cities imaginable, and this is the area where the Kuriotates shine. They have one of the best leaders in the game and they set up very fast. The city limit means that they can't compete with the big boys in total economic power, but a builder game with them is a very enjoyable experience.
The Sidar. The sidar super specialists mean that you will have cities that are the envy of the world, and they can be obtained peacefully by stockpiling priest or arcane units (Veil priests in particular). Play a standard builder game, but enjoy creating the greatest city or cities in the world at it's core. The bad point of the Sidar is that the lack of financial, or any mechanic other than the Shades means that the rest of their empire will be fairly lacklustre, and in my experience the top factions will set up faster and continue to be better overall.
The Calabim under Flauros. Financial aristograrianism, but on a civilization that converts population into production (governors manor) means that the Calabim are excellent builders in every way. And outside of the builders, they have one of the best military forces in the game in the form of vampires. If part of the building game that you enjoy is setting up an unbeatable military defence force, then Calabim might be one to consider. As pure builders though they're probably a little way behind the true top dogs, being more focussed on population increases than finances.