There are giants and there are Nephilim Giants. I remember seeing a normal one at a fairground show once. Billed as "George The Gentle Giant", this guy stood about 8 or 9 feet tall and was dressed in a kilt and tee-shirt (quite funny as I remember) you had a full view of his arms and legs which were huge, he was slow and clumsy in his movement, gentle willed and good natured and that's the way I would think of the normal giant.
The Nephilim were an entirely different creature altogether. These things were monsters physically and mentally. Their existence on this planet was recorded in books such as the Bible and the book of Enoch, and in more recent history archaeologists have discovered human skeletal remains that measure up to an amazing 36 feet long. These things were huge. Secondly, they were very agile, fast, and strong. Indian folklore has it that giants once existed on their land that could run after and catch a buffalo, pick it up and rip it's leg off, and do this while still running!, that's a pretty accurate description of the Nephilim, a predator and hunter, very destructive and very, very evil.
Anyways, somewhere back then they seem to have either wiped each other out in a civil war or have been destroyed in a global flood. That much we know as historical fact. The next point of this article is a little more tricky as it discusses the return of the Nephilim Giant to the earth, the possibilities and evidences. There are some very good books to read on this but you must have a certain amount of open mindedness to the possibility of the Supernatural or paranormal as I think it's the only way that you will understand them.
They are fallen angels which are known as demons, and demons are said to take many forms so from that point of view it would be a possibility that they are here now or could arrive in the future but in different forms (which could also explain Aliens, Reptilians etc). However they may appear, the point is that it's the same demonic spirit
For further reading and references on the subject visit: http://www.squidoo.com/NephilimGiants You will also find some helpful videos, links and images. you are welcome to leave comments and feedback too.