What are some resources that will help get me up and running quickly with the Excel interop in C#?
The article Understanding the Excel Object Model from a Visual Studio 2005 Developer's Perspective by Ken Getz covers the Excel object model in detail. Code examples are in both VB.NET and C#.
Some important caveats are covered in C# and VBA: Like Oil and Water, also by Ken Getz.
I would also see the article: How to build an Office COM add-in by using Visual C# .NET.
HTH...