I've been spending a lot of time in TeamCity lately and the duplicates finder and FxCop build runners have been fantastic. I've also got build targets in the projects for StyleCop so violation of these rules is being surfaced and I've integrated NDepend which produces some great metrics.
What other tools have people successfully integrated with TeamCity? There's plenty around that integrate into the IDE or run locally (as discussed in this question) such as ReSharper, but obviously to run on the build server it needs to be able to execute unattended and produce artifacts that can be surfaced in the build report. What options are out there that I might have missed so far?