These are the companies, and organizations who are doing interesting things with DNS APIs. If they have an API, I'm working to profile, and provide machine readable indexes of each one below.

Akamai Technologies, Inc. is a content delivery network or CDN and cloud services provider headquartered in Cambridge, Massachusetts, in the United States. Akamais content delivery network is one of the worlds largest distributed computing platforms, responsible for serving between 15 and 30 percent of all web traffic. The company operates a network of servers around the world and rents capacity on these servers to customers who want their websites to work faster by distributing content from locations close to the user
Billing Center
Case Management
Connect API
Content Control Utility (v2)
Content Control Utility (v3)
Diagnostic Tools
Enterprise Threat Protector
Event Center
Image Manager
Log Delivery Service
Network Lists
Prolexic Analytics
Property Manager
SaaS Registration
Secure Provisioning
SecureHD Policy Editor
Security Monitor
Service-Level Agreement API
Site Shield
Traffic Management
Traffic Management Load Feedback
User Admin
ARIN offers public access to ARIN registration data via a number of services. Traditionally, these services are known in the industry as Whois in reference to the public data service of the ARPANET, precursor of todays modern Internet. Whois services are offered by all the Regional Internet Registries (RIRs), most Internet Routing Registries (IRRs) and most domain name registries and registrars.
Autonomous System Numbers (ASNs) API
Customers API
Network API
Organization API
Point of Contact (POC) API
Reverse DNS API
CloudFlare, Inc. is a U.S. company that provides a content delivery network and distributed domain name server services, sitting between the visitor and the CloudFlare users hosting provider, acting as a reverse proxy for websites. Its network protects, speeds up, and improves availability for a website or mobile application with a change in DNS.
App Subscription API
Custom Pages for a Zone API
Custom SSL for a Zone API
DNS Records for a Zone API
Firewall access rule for a Zone API
Keyless SSL for a Zone API
Organization Invites API
Organization Members API
Organization Roles API
Organization-level Firewall access rule API
Organizations API
Railgun API
Railgun connections for a Zone API
User API
User Billing History API
User Billing Profile API
User-level Firewall access rule API
Users Invites API
Users Organizations API
WAF Rule Groups API
WAF Rule Packages API
Zone Analytics API
Zone API
Zone Settings API
Zone Subscription API
DNS Made Easy
DNS Made Easy’s API is available to perform core functions of the DNS Made Easy web interface programmatically. DNS Made Easy’s API is a powerful resource and a great alternative to DNS management through our conventional web interface. Use of the REST based API is available free to all Business and Corporate Memberships.
DNS Made Easy Managed DNS API
DomainTools offers the most comprehensive searchable database of domain name registration and hosting data. Combined with their other data sites such as DailyChanges.com, Screenshots.com and ReverseMX.com, users of DomainTools.com can review millions of historical domain name records from basic Whois and DNS information, to homepage images and email settings. The Companys comprehensive snapshots of past and present domain name registration, ownership and usage data, in addition to powerful research and monitoring resources, help customers by unlocking everything there is to know about a domain name.
Brand Monitor API
Domain Profile API
Domain Search API
Domain Suggestions API
Hosting History API
IP Monitor API
IP Registrant Monitor API
Name Server Monitor API
Parsed Whois API
Registrant Monitor API
Reverse IP API
Reverse IP Whois API
Reverse Name Server API
Reverse Whois API
Whois History API
Whois Lookup API
Dyn helps companies monitor, control, and optimize online infrastructure to improve end-user experience. Their Internet performance product suite includes Dyn Internet Intelligence, IP Transit Intelligence, Traffic Director, and DNS APIs. Dyn provides enterprise level sales and pricing for their DNS, and email services.
Dyn Internet Intelligence API
Dyn Managed DNS API
Dyn Remote Access API
Google Inc. is an American multinational corporation specializing in Internet-related services and products. These include search, cloud computing, software and online advertising technologies. Google provides search and advertising services, which together aim to organize and monetize the world’s information. In addition to its dominant search engine, it offers a plethora of online tools and platforms.
GSLB.me comes with a fully-fledged REST-based API to manage your DNS services. Using the API you can add, modify, delete, enable and disable domains (GSLB.me refers to DNS domains as “zones“) and records. You can also manage your geohosts and more features are scheduled for next releases.
GSLB.me Geohosts API
GSLB.me Metrics API
GSLB.me Records API
GSLB.me Reporting API
GSLB.me Zones API
Microsoft Azure
Microsoft Azure is a cloud computing platform and infrastructure created by Microsoft for building, deploying, and managing applications and services through a global network of Microsoft-managed datacenters. It provides both PaaS and IaaS services and supports many different programming languages, tools and frameworks, including both Microsoft-specific and third-party software and systems
DNS Management API
Rackspace is a recognized leader in the IT hosting market. We deliver enterprise-level managed services to businesses of all sizes and kinds around the world. Serving more than 14,000 customers in eight data centers worldwide, Rackspace integrates the industry’s best technologies and practices for each customer’s specific need and delivers it as a service via the company’s promise of Fanatical Support®. We serve as an extension of our customers’ IT departments, enabling them to focus on their core business. We got started in 1998 and since then Rackspace has grown more than 50 percent a year. There are currently 2,000 Rackers around the world serving our customers.
DNS Domains API
DNS Limits API
DNS Records API
DNS Subdomains API
Rackspace Cloud DNS
Reverse DNS API
Zerigo makes DNS worry-free. With a REST API, user-friendly interface, and industry-leading advanced security and features, Zerigo DNS makes DNS easy and efficient.
Hosts API
Zone Templates API
Zones API