Softest worsted weight yarn for a scarf?

[Boredom Becomes Me]

A great friend of mine has been helping me out a lot lately and I want to knit a combinations of scarves I know he likes. The perfect scarf. I need suggestions for a really, really soft worsted weight yarn.

I suspect the scarf will be worn more inside than out, so the yarn doesn't have to be weather proof really at all.

Thanks!