OVH servers include a pretty efficient DDoS protection. It was the only option for hosting my online game servers that didn't cost tens of thousands.

Akamai has Prolexic...it is what kept GitHub up.

Not free (actually, quite expensive imo), but one of my clients used Qrator. Don't know if it is any better or worse than CF.

If you run your own BGP routers you can use Voxility, Incapsula or a number of similar services.

Any of the CDN providers (eg Akamai) offer this. Cloud providers as well

There are many others for example Imperva, Akamai and Verisign.