Please vote for this feature if you think it is useful and it may make it into VS 2012.
https://connect.microsoft.com/VisualStudio/feedback/details/529982/group-related-files-when-they-are-open-in-different-tabs Basically the idea is to (as an optional setting) group related files (.aspx, .aspx.cs, .aspx.designer.cs) when they are open in different tabs so that they are always next to each other.
