comma before present participle: It is good, sitting here in the sun.

[navi]

1-It is good sitting here in the sun.
2-It is good your helping us.
3-It is good you helping us.

Which of these sentences need a comma after "good"?

I think "2" needs one. "3" might be considered incorrect by some people. In any case it could use a comma. The first one would be correct with or without a comma.

 

[Tazzler]

The second and thirs sentences are awkward. We would rather say "it is good that you are helping us" using a clause. The infinitive sounds better to me than the gerund/participle in the first centense. And in my opinion no commas in any of them.

 

[WildWest]

I think in the first sentence a comma placed immediately after good would indicate, at least to me, that the following group of words describe what is good.

"It's good, sitting in the sun," (=Sitting in the sun is good)(=It's good to sit in the sun)

Just imagine the speaker pausing for a second, and then makes clear what is good, bad, important etc. from his point of view.

I remember this was largely discussed in a thread. In fact, there must be some special name in grammar for such constructions. Lastly, here is another example from an episode of This American Life called It'll Make Sense When You're Older:

"At first, it’s super annoying, getting told it’ll make sense when you’re older."

As for the third, I remember that in one of the episodes of Gossip Girl, Dan say the following to Nate:

"It means a lot, you getting involved."

 

[natkretep]

The structure in the second and third sentences is sometimes called right dislocation. See Dislocation (syntax) - Wikipedia

In syntax, dislocation is a sentence structure in which a constituent, which could otherwise be either an argument or an adjunct of the clause, occurs outside the clause boundaries either to its left or to its right. In this English example They went to the store, Mary and Peter the dislocation occurs to the right.

This occurs mainly in speech, and I don't find it awkward.