In the last few days I've found a tool called Gendarme it is an open source tool from the Mono Project that allows you to find problems in .Net (either Mono or Microsoft.Net) applications and libraries.
It has a rule based system to do the analysis and it can be seen as an FXCop/Team System Code Analysis kind of system.
I haven't counted the number of rules it provides but doing a visual analysis it doesn't seem to have as many rules as Team System Code Analysis. However quantity isn't everything and from my analysis it has a pretty number of good rules (including some categories that the Code Analysis doesn't has like Linq)
The rules are grouped in the following categories
You can see the full list (and description) of the rules here
There is no Visual Studio integration so you either have to run it from the command line or from a supplied windows form wizard. No MSBuild integration exists either but it would be fairly easy to implement a custom action or just call the execute task.
Integration with TFS could be either easy or hard depending on how fully integrated you would want it. Since the execution of Gendarme produces a report (XML,HTML,etc) you can execute on your build process and make the HTML report available on the build results (the easy part) or if you want full integration like having the data directly on the TFS build warehouse that could a lot more work.
I've spent a couple of hours running it on a median sized project and it enabled me to fix some naming mistakes, make the code more clear in some areas and even fix an error where disposed wasn't being called.
During my analysis I also found a bunch of false positives. The tool has a feature that categorizes the issues that it has found with a degree of confidence, which states the degree of confidence that the rule has in the face of the found issue (most false positives had a medium to high degree of confidence which is a bummer).
The rules documentation is complete and allows you to understand the consequence of not implementing the rule and why you should fix the found issue (although some rules are not documented).
Definitively a tool to use in the future.
[cross posted on http://agilior.pt/blogs/tiago.pascoal/archive/2008/12/29/6537.aspx]