• Clause
• Conversation Analysis
• Discontinuity (Grammar)
• Discourse Marker
• Parenthesis
• Repair
• Tag Question
• Verbal Hedge

Examples and Observations:

• "Commonly occurring examples [of comment clauses] are I'm sure, I'm afraid, I admit, I gather, I dare say and you see, you know, mind you, you must admit. Many comment clauses are stereotyped fillers which are inserted into running speech in order to establish informal contact with the hearer. When the subject is realized by I, their function is to inform the hearer of the speaker's degree of certainty (I know/I suppose) or of her emotional attitude to the content of the matrix clause."
  (Carl Bache, Essentials of Mastering English. Walter de Gruyter, 2000)

• "As you know, the concept of the suction pump is centuries old. Really that's all this is except that instead of sucking water, I'm sucking life."
  (Christopher Guest as Count Rugen in The Princess Bride, 1987)
• The presentation went quite well, I believe.
• "All time is all time. It does not change. It does not lend itself to warnings or explanations. It simply is. Take it moment by moment, and you will find that we are all, as I've said before, bugs in amber."
  (Kurt Vonnegut, Slaughterhouse-Five, 1969)
• "Instead of parenthesis Quirk et al. (1972: 778-789) introduce the term 'comment clause,' disjuncts or conjuncts which 'may occur initially, finally, or medially, and have a separate tone unit' (ibid.). The following five subtypes are identified: main clause (I believe), adverbial clause introduced by as (as you know), nominal relative clause (What's more), to-infinitive clause (to be honest), -ing clause (speaking as a layman).
  
  "To this list -ed clauses (Stated bluntly) are added by Leech and Svartvik (1975: 216-217), who also gave a brief functional description of comment clauses: they 'are so called because they do not so much add to the information in a sentence as comment on its truth, the manner of saying it or the attitude of the speaker.'"
  (Gunther Kaltenböck, "Spoken Parenthetical Clauses in English: A Taxonomy." Parentheticals, ed. by Nicole Dehé and Yordanka Kavalova. John Benjamins, 2007)

• Fly high above the clouds
  On the wings of a dream
  I hear your whisper loud--
  Or so it seems.
  (Jackie Lomax, "Or So It Seems")
• "The comment clausesyou know and you see require some kind of response from the listeners which, in a narrative turn, are more likely to be paralinguistic than vocal. Nods of the head, direct eye contact and minimal vocalisations like mm will satisfy the speaker that he still has the audience's consent to continue dominating the turn-taking."
  (Sara Thorne, Mastering Advanced English Language. Palgrave Macmillan, 2008)
• "In an example like Margaret Thatcher is now a life Baroness, which everyone knows, we can replace which with as with virtually no change of meaning. But unlike which, as is not generally used as a relative but as a conjunction. Note also that as everyone knows is positionally less restricted than which everyone knows: it could also be placed initially or medially. We therefore do not classify such an as-clause as a sentential relative clause but as a comment clause."
  (C. Bache and N. Davidsen-Nielsen, Mastering English. Walter de Gruyter, 1997)