I'm a fan of Sentry, and their hosted service is very affordable. The fact you can push data to it on your own terms is great. I use it in combination with Logs

I'm a fan of Sentry, and their hosted service is very affordable. The fact you can push data to it on your own terms is great. I use it in combination with Logstash as an output, so any logged errors reaching Logstash are automatically piped to Sentry. As a bonus, should you wind up deploying Sentry internally, you need only update the API host in Logstash.