I have been meaning to make ketchup for quite some time. I ran out the other day and since necessity is the mother of invention, I was gave it a shot.
I got my recipe here: http://www.instructables.com/id/Ketchup-Catsup-Recipe/
I didn't have any allspice but other than that I followed the recipe (my agave nectar wasn't blue, it was Light Madhava). I really liked it and more importantly I put it in an old ketchup bottle, threw it in the fridge, and the kids didn't notice a difference. Bonus.
I like the fact there is no corn syrup in it, I can pronounce all the ingredients, and I can control how much sugar/salt it contains!