These cycles are not so much traditionally published works as they are groups of stories with similar themes. As far as stories concerning the Dagda, the Mythological cycle (which we admit has a confusing name) has lots of descriptions of the Tuatha Dé Danann (The Children of Danu), as well as the stories of the two battles of Mag Tuired (see the Dagda's Wall and Campaign Notes for more on this). Though these stories are all very old, the oldest existing collections of them date back to the 12th century.
Comics love mythology. We cannot love comics enough for this. The Dagda's first appearance on the Marvel scene was in 1989, in an issue of Thor. He's appeared in occasional Marvel comics ever since, though not as regularly as his hammer-wielding Norse bro.
Let us tell you, if you want your daily dose of mythology, turn to Mike Mignola's Hellboy. In the series, the Dagda is the High King of the Tuatha De Danann. He's old and powerful and more of a watchful figure than the active warrior of the old stories. We think this works well, though—we imagine the Dagda would probably be a lot like this after thousands of years.