Is there an AWS AMI for node.js?

There isn't a specific pre-canned AMI, but you can install node.js in an instance based on a suitable AMI and then shrink-wrap your new build into an AMI of your own.

You can install on the standard Amazon Linux AMI. For development and low traffic the micro-instance is great/low cost.

If you want a ready-to-go install check out No.de - sign up and generate a coupon. Free for now as well.

You can use the free images built and maintained by StrongLoop. There are images for stable versions of node, for every region. You can search for "StrongLoop" under images. Latest version of node on these images is 0.10.26.

USWest Oregon       -  ami-14d5bf24,     
USEast              - ami-6541590c,        
USWest N California - ami-5a3e061f,  
Ireland             - ami-f154ae86,  
AP Singapore        - ami-5a7f2c08,  
AP Tokyo            - ami-3d2a513c,  
AP Sidney           - ami-b5178f8f,  
AP Sao Paulo        - ami-1919bb04, 

Along with node, these images also have StrongLoop cli tools which can be used to simplify the deployment of node apps to AWS EC2.