When trying to debug a ASP.NET MVC app, the breakpoints in my controllers arent getting hit. When entering debug mode they just show an empty red circle with a warning trian
Few more possibilities:
If you have a client and server in your solution (lets say a WPF and WCF app) you should make sure you select 'multiple startup projects'. [this one is similar to your accepted answer, but useful if you need a client running too]
Release mode is selected for the project. When doing a fresh get (as I discovered today) on a new machine VS seems to like to switch to 'Release' configuration profile.