8 sand. I ask for "plasterer's" sand, though it may be called mixed building sand elsewhere. It's a mix of sharp and soft.
2 lime. Any hydrated lime.
1 cement. I use Mastercrete. I'm convinced it dries to a slightly darker colour than Blue Circle Ordinary Portland Cement. I also suspect that the additives it contains make it easier to use. I also like the fact it can be stored outside.
I find putting a 1.5 buckets of water in the mixer first gives a good consistency, which can be adjusted if necessary.
The advantage of this recipe is that it's about as cheap as you can get, and looks just as good as more expensive mortars.