What is the Biblical basis for "righteous anger"? What would be defined as "righteous anger"?

Ephesians 4:26 (ESV) says:


26 Be angry and do not sin; do not let the sun go down on your anger,



So, is all anger justifiable if you don't sin? Or are there other verses that address this subject? When is anger justified?
This is consistent with other verses like James 1:20. 


  because human anger does not produce the righteousness that God desires.


Basically they are saying that you aren't going to do anything good when you are angry. One can be angry but one's actions will tend towards sin in these situations.