I was searching a couple of days back for a tool that would generate dependency matrices for C# code. I didn't find free ones, but I did find a plugin for Lutz Roeder's Reflector that will do this for compiled assemblies, which is just as good. I haven't done a fresh install of reflector for quite some time and didn't know it supported add-ins, but it does and there are a few good ones.
The dependency matrix tool is absolutely fantastic, and I highly recommend it. Amongst other things it will generate a report that includes cyclic dependencies. Just that is worth its weight in gold. Cyclic dependencies typically creep in when you make short cut kludges to hack in some inappropriate type-dependent logic into a class. As such, its usually an indication of a design break, and it also makes unit testing harder. Use this tool, look at any cycles it reports, and fix them. Your code will be better as a result.