C/C++ = Visual Assist X.
For me, C# = ReSharper + Visual Assist X.
Needless to say, ReSharper is much more powerful for C# development, than VA. But there are some features, like ability to show just methods in suggestions list, or highlight nearest scope that are in VA, but no equivalent in R#. I use both. Looks like they live pretty well together: i use default settings for VA, and i had to select ReSharper-->Options-->IntelliSense-->General-->Visual Studio to enable VA version of IntelliSense instead of ReSharper's one.
I also customized identifiers colors in ReSharper, now they look like VA default colors, but show additional information (like Mutable Local Variables are bold).