Mark Goodacre posted a podcast entitled "Who is this 'Son of Man'?" over at NT Pod in early April. I have finally had time to listen to it, and as usual, he has done an excellent job introducing a NT topic (which is why I continue to make use of his podcasts in class). Goodacre points out that "the Son of Man" (ὁ υἱὸς τοῦ ἀνθρώπου) was only spoken by Jesus and it is almost non-existent outside of the Gospels. So what did the phrase mean to Jesus? what did it mean to his followers? and why did early Christians essentially not use it? Such questions are why there is no end to scholarly discussion on the topic.
I recognize that Goodacre is only giving an 11 minute introduction to a complex topic, but I did want to clarify a couple points. The Jewish Second Temple text the Similitudes of Enoch does make reference to a son of man figure and there are clear indications that Daniel 7 has influenced this text (chs. 46-48). Although Goodacre states that Similitudes is possibly later first century and after the time of Jesus, recent Second Temple scholarship has reached a consensus that the text is late first century BCE or early first century CE. Thus, it is plausibly prior to (or contemporary with) Jesus and therefore plausibly evidence of Jewish messianic understandings of the Danielic "one like a son of man" during Jesus' lifetime (see Boccaccini, ed., Enoch and the Messiah Son of Man).
Goodacre also mentioned that 4 Ezra speaks of "the son of man". This late first century text does reinterpret the Danielic son of man figure (see chs. 11 and 12), but 4 Ezra does not refer to "the son of man" or even "one like a son of man". The term used is a "something like the figure of a man" (13:3; Metzger's translation in OTP). I realize this is splitting hairs for some, but some scholars do make this a significant point. However, 4 Ezra does highlight the way in which it is the human-likeness of the visionary figure that Daniel draws attention to.
Again, I recommend listening to the podcast for a great introduction to this perennial NT topic.