I like how well-thought-out the licence revocation clause of the AOMedia patent licence is. It takes effect when a licensee sues over an implementation specifically over the relevant patent claims--so lawsuits unrelated to these patent claims are allowed (so if you infringe on other patents but also implement the licensed patent in the same implementation, the rights holder of the other patents can sue you over those claims without losing their licence)--and there is also a carve-out for counterclaims, and lawsuits to enforce this licence.

But I am not sure if the first exemption is necessarily a good thing. The Apache License, Version 2.0 is broader in what may be grounds for patent licence termination. So it is a better deterrent against patent trolls (even if that means some legitimate patent claims are also discouraged).