Michael Drout has just finished his excellent series on dating Beowulf*. I recommend it.
Since Drout would call himself a late dater moving early, and I would call myself the reverse of that, I'm not sure how valuable a distinction "late date" and "early date" is when talking generally. Obviously, the surviving manuscript is late, and obviously the historical source material is early; I don't know anyone who claims that the manuscript was written in, say, the 6th Century, or that the historical Hrothgar lived in the 11th. When we are talking about the "date" of Beowulf, then, we are have a moving target, and what we mean by "date" might mean something entirely different depending on the context. A few times I've heard two scholars arguing about the date, only to realize that they were arguing past one another. I suppose that is the reason there is so much disagreement; half the time, we can't even agree on what we are disagreeing about.
Every year, about 3000 medievalists attend the Medieval Congress at Kalamazoo, and every year they bring about 6000 different opinions on the dating of Beowulf with them.
*Er, by "dating Beowulf" we mean figuring about a date of composition of the poem, not about courting the Geat romantically. Not that you should be discouraged; I'm sure he's a very handsome man.