New Relic is web application performance management tool for Your dedicated server or VPS.
It supports PHP, Java, Ruby, Python and .NET web applications.
With New relic You can easily find out problems in a server because it sorts all problems by importance and shows what is more important.
New Relic has decent MySQL database monitoring features which can help You find tables which are used the most and which needs attention the most. It also shows slow queries. It also supports NoSQL but I don’t have any apps which use it so I don’t knwo how good is NoSQL support.
If You don’t have basic server resource monitoring yet on Your server You can also enable CPU, Disk, Memory and Network monitoring with nice historical data.
The best thing about New Relic is that both web app management and server monitoring are very easy to install. It took me 5 minutes from installing both services to start checking out fancy graphs about my server performance on their website 
I am little lazy to explain all the cool stuff about this service so take 10 minutes of Your time to register:
http://newrelic.com
When creating Your free account You automatically get trial of PRO version for 15 days after which You can continue to use free version.
Here are some screenshots from my server:
http://imgur.com/a/eAuFU
