First of all, there is no such thing as data binding in ASP.NET MVC. You have to pass select values from the controller to the model either using a view model, or via ViewBag (or ViewData if you still use MVC2). Here is a good "howto": http://www.mikesdotnetting.com/Article/128/Get-The-Drop-On-ASP.NET-MVC-DropDownLists
], but google can give you more.
And now with cascading.
There are several approaches, but these can be interesting:
1) If you know all your lists on the first render of your page, you can embed them in the view as JS arrays, and filter them on client side - this is not dynamic and can be a huge overhead.
2) Embed your "cascading" logic into the view: Simple Implementation of MVC Cascading Ajax Drop Down
], but I don't recommend this, because it is not following the MVC concepts.
3) Using a Jquery, making an ajax callback to populate the second (and following) lists. I found a plugin, you might use: http://weblogs.asp.net/rajbk/archive/2010/05/20/cascadingdropdown-jquery-plugin-for-asp-net-mvc.aspx
] - I reccomend this approach, since you can dinamically calculate what elements to put into the list, and you don't need to refresh the page.