KV is the obvious one but Durable Objects themselves have interesting persistence properties. There is a sqlite DB service called D1 landing and there is an object service called R2 which is is actually really nice. Also there is a new queuing service which is also fully persistent, even if queues are a non-traditional persistence mechanism.
However Workers is a strange runtime and has strange billing/pricing. I wish there was better visibility into the "bundled" vs Unbound pricing models, namely I wish it could just tell you how much it would cost if you switched from bundled (this bitching could be specific to Enterprise plans though so YMMV).
Overall I'm pretty happy with it in a professional context. Cloudflare's network is second to none. The rest of their stuff... I could do without but Workers and the world's best edge makes up for it's other shortcomings.
