There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men...." Genesis 6:4
This is one of the most interesting verses in the bible. Who were "the sons of God" who had sex with "the daughters of men"? Jesus and his long-lost brothers? Sex-crazed angels from hell?
The bible doesn't say, but whoever they were, they seemed to have pissed off God. Because in the very next verse, he decides to kill every living thing that he had made.
When Joshua sent twelve spies to "spy out the land of Canaan" they came across "men of great stature", "giants", even.
The land, through which we have gone to search ... all the people that we saw in it are men of a great stature. And there we saw the giants, the sons of Anak, which come of the giants: and we were in our own sight as grasshoppers, and so we were in their sight. Numbers 13:32-33
The Emims dwelt therein in times past, a people great, and many, and tall, as the Anakims; Which also were accounted giants...." Deuteronomy 2:10-11
That also was accounted a land of giants: giants dwelt therein in old time; and the Ammonites call them Zamzummims; A people great, and many, and tall, as the Anakims; but the LORD destroyed them. Deuteronomy 2:20-21
Og's bed was nine cubits long -- large enough for a 4 meter-long giant. 
For only Og king of Bashan remained of the remnant of giants; behold his bedstead was a bedstead of iron; is it not in Rabbath of the children of Ammon? nine cubits was the length thereof, and four cubits the breadth of it. Deuteronomy 3:11
Goliath was about 10 feet tall (~3 meters).
Goliath, of Gath, whose height was six cubits and a span. 1 Samuel 17:4
Ishbibenob was a son of a giant. He had a spear that weighed 300 shekels (~3.5 kilograms).
Ishbibenob, which was of the sons of the giant, the weight of whose spear weighed three hundred shekels of brass in weight. 2 Samuel 21:16
Saph was also a son of a giant.
Sibbechai the Hushathite slew Saph, which was of the sons of the giant. 2 Samuel 21:18
And there was yet a battle in Gath, where was a man of great stature, that had on every hand six fingers, and on every foot six toes, four and twenty in number; and he also was born to the giant. 2 Samuel 21:20
Among those killed by Benaiah, was an Egyptian five cubits tall. (7.5 ft, 2.3 m).
Benaiah ... slew an Egyptian, a man of great stature, five cubits high. 1 Chronicles 11:23
God destroyed the Amorites who were a race of gaints as tall as cedars and as strong as oaks. Amos 2:9