The FxCop team recently released a new version, 1.312. Check it out.
I've been working quite a bit lately with the guys responsible for this technology. They've poured a lot of energy into this product... and it shows. With this release, you can expect improved quality of existing rules (reducing false positives, increasing coverage), and a number of entirely new rules. This stuff is based entirely on real experience shipping managed code and is a great way to avoid common implementation mistakes and pitfalls. And it helps you to be consistent with the Framework, too, a real plus when you're shipping publically-consumable APIs.
If you're not already shipping FxCop'd code, I'd highly recommend it... :)