One of the big ones to me is "move class to its own file". Means when you are sketching up some multi-class API or something you can just type away in a single source file, and as soon as something looks half-finihshed I just alt enter and it creates a new file with the correct name and moves the type to that file including adding the necessary imports to the header. A lot of context-switch time gained.
Next big thing is navigation. Go to type, go to symbol and go to file are super quick and means I never go to the source tree to navigate the solution.
I didn't find the "move class" feature while I was trialing, but it does sound pretty handy.
Symbol search is incredibly useful, that was a revelation when somebody told me about it. But Visual Studio has had that since at least 2010, I think maybe 2008. Resharper's is a bit more complete, but I think the VS built-in one is a bit faster. The VS native implementation is Edit -> Navigate To, the default key combo is ctrl-comma, but I think Resharper takes that combo for its own purposes.
Next big thing is navigation. Go to type, go to symbol and go to file are super quick and means I never go to the source tree to navigate the solution.