What can I use for good quality code coverage for C#/.NET?

I use the version of NCover that comes with TestDriven.NET. It will allow you to easily right-click on your unit test class library, and hit Test With→Coverage, and it will pull up the report.

An alternative to NCover can be PartCover, is an open source code coverage tool for .NET very similar to NCover, it includes a console application, a GUI coverage browser, and XSL transforms for use in CruiseControl.NET.

It is a very interesting product.

OpenCover has replaced PartCover.