Examples of using "いい案だ!" in a sentence and their english translations:
What a nice idea!
- What a good idea!
- What a nice idea!
That's a great plan.
Good idea!
That's a good plan.
- That's a good idea!
- That is a good idea.
- That's a good idea.
- That's a good idea!
- That is a good idea.
- That's a good idea.