There are certain tasks that a web developer will across many times, and that often take more time and thought than they should.  This is my list of items I often come across that I wonder why I don't have a better solution in place...

Grid Sorting and Paging

Client-side and server-side.  If the data is not too large handle all sorting and paging on the client.  Otherwise, write your back-end code to handle AJAX post-backs for each page of data.  To avoid special queries and stored procedures try populating an in-memory list and writing your sorting/paging routines on that list.

Validation

Gone is the day of drag-and-drop validation controls in ASP.NET.  The just cloud up your html pages.  Yes, they do server-side validation, but are you testing that like you should... probably not.  Validation can be wrapped up in client-side and server-side objects or classes.