I know there's Bungle in the Jungle and some other H/Hr long winded story where they both turn into wolves and kill Voldemort, but I'm drawing a blank on more, surprisingly.

 

In The Many Deaths of Harry Potter, he doesn't so much kill them as a mongoose, but he does have to fight them, and he uses his animagus form as a strategic advantage.

 

In a somehow convoluted way, you could add A Black Comedy to the list.

 

Once upon a time, I wrote a really bad story, worse than normal, that features Harry destroying death eaters at the 4th year graveyard scene with his animagus form. Here's a direct link to the chapter, since I would not recommend actually reading the story - https://www.fanfiction.net/s/5469784/14/Harry-Potter-and-the-Unexpected-Changes

 

Luna's Hubby

 

Weres Harry

Harry is a werewolf animagus. Sort of.