Does God stay angry forever?
No – Psalm 30:5 – This is poetry, not theology. But, when read in context with the rest of the Psalm, it does show the example of someone (David) turning back to God and God’s anger ceasing.
Jeremiah 3:12 – Continue reading verses 13 & 14 to complete the thought. God’s anger is conditional and ceases when guilt from sin against Him is acknowledged.
Micah 7:18 – The complete thought is needed. Reading verses 16 & 17 shows that the nations’ returning to fearing God assuages His anger.
Yes - Jeremiah 17:4 – Refer back to Jeremiah 3: 12-14. God’s anger is based on the actions of the people. In 17:4, He is speaking of the future consequences of their continued refusal to obey His commands. He is warning that His anger will last as long as their pursuit of sin. **Some more interesting thoughts here: http://www.tektonics.org/gk/godangry.html
Malachi 1:4 – Another example of God stating what will happen based on these people refusing to turn back to His ways. It’s the same warning of his anger lasting as long as their pursuit of sin.
Matthew 25: 41, 46 – These verses refer to the final judgment for those who refused to turn to God before they died. They have to do with God’s justice and punishment for sin, not anger.
All these examples, except Matthew 25: 41, 46, refer to God’s reaction to obedience or disobedience. Kind of like, “If you do X, then Y will happen.” God’s anger will last as long as the sin.