I'm using the SSM Parameter Store [0] a lot, because of its easy integration in applications – many services can directly pull secrets from it and provide them as environment variables. The secrets can be KMS encrypted and cost a fraction of the Secrets Manager, which I think is just the parameter store with secrets being rotated by a Lambda.
It also has a pretty generous free tier, so if you're not using very ephemeral creds and you don't need auto rotation, it's a fantastic option (disclaimer though I work at SSM and am biased - glad to hear you also like the product :)
[0] https://docs.aws.amazon.com/systems-manager/latest/userguide...