As you can tell from the link worachj provided, the 1800 series pop-ups are still produced by Rainbird.
As for height, the recomendation I've read regarding lawns is that you don't want anything shorter than 4". The only options taller than 4" is 6" and 12", and I would think those would only be needed in special situations.
So generally speaking, you want to get 1804 series.