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!