We have a simple integration API and we can also integrate with any system that can send email. Regarding the integration, just shoot us an email: support@pagerduty.com.
Was looking for it too, found it: http://www.pagerduty.com/docs/api/api-documentation took a while, though -- in my opinion, a link to the API documentation is important enough to put in the footer, maybe next to or under "integration guides".