I own nearly all of the Eberron books and a great deal of the FR ones. And Dragonlance, but I only got that because our DM was running there and I had to have it...
Anyways, the ECS really rocked my world. And Sharn: City of Towers was possibly my happiest Eberron (and possibly D&D) purchase to date. Not only did it include things like religious and secular holidays and festivals, dozens of plot hooks, cultural quirks, and more locations for adventure in one city than I've seen in some whole countries, it also included the Eberron soundtrack CD. Fabulous.