The Atkins ketchup is pretty good, and thicker than the Jok'n'Al.

I think they're all pretty darn sweet, though, and in the end I like the Westbrae "Un-Ketchup" which isn't sweetened at all and has a very nice thick tomato-ey flavour.

Usually found in Health Food Stores (and bonus, costs a bit less than the 'low carb' ketchups).