Really, none? IDK, I've always thought DynamoDB and S3 were amazing, and Lambda, albeit not perfect on launch, was highly innovative and useful for many, many, many circumstances you'd either needs a k8s cluster or fleet of little used servers at the time.

SQS and Cloud watch were legit to, although cloud watch metrics are a bit aged and logs were really difficult to use until insihhts came into place

Also Glue, while it has some tenancy issues and rough edges, takes a bunch of work out of managing a datalake

Oh and Aurora + Aurora serverless weren't as flashy but from an ops perspective game changing at the time

Cloudformation is definitely showing it's age and I hate writing it compared to CDK, but it was also pretty game changing at the time. I don't know if it was the first infrastructure as code language, but it definitely kick-started the revolution.

Amazon the shopping website is useful and reliable at least.