Here is the biggest giant model I have. I just picked him up last week when Miniature Market was selling him at 50% off during one of their daily deals. It is a limited edition Pathfinder Rune Giant from the pre-painted Pathfinder Battles line of miniatures. This one is really nice. You probably won't find too many of them at the $30 price point I got mine at. Miniature Market sold out of them very quickly the morning they were put on sale.
Anyway, here he is next to a few other Giant Models I have and a few resolute Empire citizens. I think the Empire troops may be a bit out classed here! Just to give you some measurements, he is 5.5" tall from bottom of the base to the top of his head. I'm guessing he'd be 7" tall if he weren't hunched over. The Sword is 6" long from the end of the pommel to the end of the blade.
Here is another with them all along the same plane to get a better idea of comparative size.
If you are wondering about the skeleton giant, it is from Reaper. It is called a Colossal Skeleton. They are doing a slightly modified version of it with different weapons for their Bones line, but it won't be available for a few months. They are just calling it Undead Giant and it will have a giant hammer instead of the big Khopesh style sword.