In terms of web development in Visual Studio, ASP.NET was the first area that was supported by ReSharper. Currently, almost every ReSharper feature supports ASP.NET in some way—both Web Forms and MVC.
In the same way as in C#, ReSharper helps you write ASP.NET by extending IntelliSense, generating code, and providing you with some refactoring methods.
IntelliSense provides you with prompts for web-related things, such as ASP.NET controls, ASP.NET MVC helpers, resources, JavaScript symbols, and so on.
While working with ASP.NET, ReSharper helps you in importing required namespaces and removing unused directives (same as with using statements in C#).
As with C#, ReSharper allows you to generate members based on the implemented interface; in ASP.NET, you can generate Content tags based on ContentPlaceHolders from your Master Page and the required event handlers.