I'm looking for an e-commerce "platform" in Java or .NET that can satisfy the following requirements:
The goal here is to integrate this with a RIA written in Adobe Flex. We are comfortable with writing a thin backend layer to support the Flex app, so the solution doesn't require a remotely-accessible API, rather just one that we can invoke from our own backend code.
I used ofbiz for some projects, a joyful experience. It's now under the apache umbrella: http://ofbiz.apache.org/
From the website:
The Apache Open For Business Project is an open source enterprise automation software project licensed under the Apache License Version 2.0. By open source enterprise automation we mean: Open Source ERP, Open Source CRM, Open Source E-Business / E-Commerce, Open Source SCM, Open Source MRP, Open Source CMMS/EAM, and so on
I used it to build an ecommerce application to sell customized products to consumers. I used the webshop part, the production planning and warehouse management.
Beware that it takes some time to dig into this huge framework but depending on your actual needs it will be worth it. There is also decent commercial support by a lot of service providers.