I found user controls to be incredibly useful when working with ASP.NET webforms. By encapsulating the code required for displaying a control with the markup, creation of reusable components was very straightforward and very, very useful.
While MVC provides convenient separation of concerns, this seems to break encapsulation (ie, you can add a control without adding or using its supporting code, leading to runtime errors). Having to modify a controller every time I add a control to a view seems to me to integrate concerns, not separate them. I'd rather break the purist MVC ideology than give up the benefits of reusable, packaged controls.
I need to be able to include components similar to webforms user controls throughout a site, but not for the entire site, and not at a level that belongs in a master page. These components should have their own code not just markup (to interact with the business layer), and it would be great if the page controller didn't need to know about the control. Since MVC user controls don't have codebehind, I can't see a good way to do this.
I've searched previous SO questions, and have yet to find a good answer.
Options so far
In an attempt to avoid turning the comments section into a discussion...
RenderAction This allows the view to call another controller, which will be responsible for interacting with the BLL and whatever data is necessary to its corresponding view. The calling view needs to be aware of the sub controller. This seems to provide a nice way to encapsulate partial views and controls, without having to modify the calling controller.
RenderPartial The calling controller is still responsible for executing whatever code is associated with the partial view, and making sure that the model passed to the partial view contains the data it expects. Effectively, modifying the partial view potentially means modifying the calling controller. Annoying especially if this is used in multiple places.
Portable Areas Place each control in its own project/area?
