When I bought a .io domain through them they tossed in a free SSL certificate. Not sure if this promotion is still happening, but it helped persuade me to go with them.

Also gandi. Their support and service are top notch (not only for domain names, mind you).

They also offer 2-factor auth and a Libcloud[1] compliant API.

[1] http://libcloud.apache.org

Agree. Some of the advantages of choosing Gandi are a free SSL certificate and free email (IMAP/POP - 1 GB).

Thirding the Gandi recommendation.

Same here, a bit pricier than other places but their "no bullshit" policy is worth it.