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When it comes down to customization ability, it's really hard to beet MODx CMS (http://modx.com). I have built everything from e-commerce sites to internal applications such as a CRM for publication company. If you don't have the development ability, they offer commercial support and have quite a few big clients they've worked with such as Dell. The real beauty of MODx is that it's designed to help you build without having to hack the core. Pretty much anything you want to accomplish, you can do so while maintaining a clean upgrade path. Hopefully this helps