I work for AppNeta, and while we directly compete against New Relic, I love what they've done for the market. Their competitors were these clunky, on-premise, hard-to-use, didn't support Ruby / Python / PHP / node.js apps, and they've built a beautiful service that's legitimately easy to use. A lot of the data is available from CA or Dynatrace, but it's so much harder to set up and use.
Monitoring so commonly focuses on server metrics, or outside-in uptime, or logs, and I really do think that monitoring transactions end-to-end is an important part of the picture. Day to day, New Relic is absolutely the competition, but in the big picture, there's a lot of big companies using technology that's 15 years old because somebody like New Relic or AppNeta hadn't come along yet.
Glad to see that the market likes them as well. There's awesome stuff happening in Application Performance Monitoring (APM), and if you're not already using something like this, I strongly recommend you look at AppNeta, New Relic, ... and not really anybody else, because the rest haven't really figured it out yet.