Some tools of the trade (what do I use and why)

Application monitoring, investigation and alerting:
AppDynamics
New Relic
JMX Trans

One off environment administration:
Capistrano

Configuration management:
cfengine
Ansible

Performance Testing:
Jmeter

Render Testing:
PhantomJS
Selenium

CI/CD and job scheduling:
Jenkins
Bamboo

Application level configuration management:
Glu

Graphing everything:
Graphite