App Hub is the website created just for Windows Phone and Xbox LIVE Indie Games developers that provides free tools, sample code, community support, and educational resources to help you develop your apps and games for Windows Phone and Xbox 360.
For a $99 USD annual subscription, you can submit your apps and games to App Hub for sale or free download in the Windows Phone Marketplace or Xbox LIVE Marketplace. The site also provides you with a personalized dashboard to manage merchandising, track downloads, and keep track of how much you’re earning. If you are a Dreamspark student the membership is free. You will need a Windows live ID to register.
Once submitted, it typically takes 3-5 business days for your app to be certified then published.
Want to hear how this process goes from someone who has submitted over 30 apps already? WMPoweruser found that Adam Nathan, who is writing a book about developing for Marketplace, has posted his experiences here.