Salesforce.com
(Contact)
Salesforce.com is a very popular cloud based CRM.
MailChimp
(List Subscriber)
MailChimp is a very popular Newsletter mailing service.
Use FoxWeave to easily Sync Contacts in Salesforce.com to List Subscribers in MailChimp
Cloudant DB

FreshBooks

Google Forms

Google Mail

HTTP

MailChimp

MongoHQ DB

MySQL DB

Oracle DB

OnePageCRM

PostgresSQL DB

Salesforce.com

Sendgrid

MS SQL Server DB

Webhooks

Wufoo

Twilio

Twitter

Zendesk