Where I work, we have found the "Email Alert Thresholds" offered by Linode to be very helpful.

Currently, all the available threshold alert notifications allow you to set a maximum acceptable value, and the comparisons are based on whether something is "exceeding" or "greater than" the setting.

I would love to see "less than" comparisons as well. In other words, set a minimum acceptable value, and be notified if the average fails to meet that minimum.

For example:

Average CPU usage over 2 hours dropping below this value triggers this alert.

Average outbound traffic over a 2 hour period dropping below this value triggers this alert.

etc.

Thanks!