What is the best web host for web businesses like Ebay?

I am planning on launching an online trading post type of site. The site will have very dynamic and interactive features such as search capabilities, image uploading, member login, and member inventory. I do know what type of web features are required to support those features. I will most likely need a lot of server space, as I am expecting a large user base of around 10,000. What is the best webhost that can meet those requirements? What is the best domain registration site?
*edit- I do *not* know what type of web features are required to support those features.