Yes there were definitely Angels that came down and created children (It is the children that are the Nephilim) that were human/angel hybrids.  I believe that one of the big reasons for the global flood was because of this corruption of the human race, which was part of Satan's plan to so corrupt the human race that Jesus, the messiah couldn't come to redeem humanity.  If you read Genesis 6 you'll see the cause:

"5Then the Lord saw that the wickedness of man was great on the earth, and that every intent of the thoughts of his heart was only evil continually. 6The Lord was sorry that He had made man on the earth, and He was grieved in His heart. 7The Lord said, “I will blot out man whom I have created from the face of the land, from man to animals to creeping things and to birds of the sky; for I am sorry that I have made them.”

I always assumed that the only reason for the destruction was that "every intent of the thoughts of his [mankind's] heart was only evil continually."  I always missed the verses right before these:

"1Now it came about, when men began to multiply on the face of the land, and daughters were born to them, 2that the sons of God saw that the daughters of men were beautiful; and they took wives for themselves, whomever they chose. 3Then the Lord said, “My Spirit shall not strive with man forever, because he also is flesh; nevertheless his days shall be one hundred and twenty years.” 4The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of men, and they bore children to them. Those were the mighty men who were of old, men of renown."

This is the verses about the "sons of God" (angels) coming down to the "daughters of men" (human women) and having children with them.  God had to wipe out the corrupted semi-humans because he would only be kinsmen redeemer of the true, God created humans.

I also used to wonder why God had Israel wipe out every man, woman and child of certain groups in Canaan.  I thought it was solely so they wouldn't be led astray, but the groups they were told to destroy were peoples that included giants, especially the rephaim.  I now believe these people were also corrupted with fallen angel DNA and that is why there was no mercy on them.  This aligns with the Scripture and seems to better align with God's character as revealed in the rest of Scripture.

Jimmy Evans, who focuses on end times prophecy, has interviewed several guys with books on the nephilim (fallen angel/human hybrids).  I actually bought two of them.  One had too much repetition and I lost interest.  "On the Trail of the Nephilim: Giant Skeletons & Ancient Megalithic Structures" by L.A. Marzulli was fascinating.  It goes through old newspaper articles mentioning giant skeletons in North America, giant henges (circular megalithic mounds) in the NE US, and amazing megalithic structures and strange skulls in South America.  I'm unsure if I agree on all of his conclusions (don't agree or disagree), but the evidence he shows is amazing.  I couldn't put the book down.