http://www.pagerduty.com/
Takes alerts from monitoring systems and sends emails, phone calls and SMS messages. Handles on-call schedules, escalation, acknowledgement, etc.
http://airbrakeapp.com/
Airbrak collects error messages from Ruby on Rails (and others via unofficial plugins) apps and collects them for review. Looks interesting. Starts at $5/month up to 4 projects, 4 users, 15 errors per minute.
