Some yarns are always pretty soft--merino and alpaca come to mind.
It also depends on what you are looking for in terms of care. Are you willing to hand-wash? Is it for a child or someone who won't hand wash? What's your price limit?
If you find a yarn that you like, maybe you can post and ask if anyone's used it to get an opinion. We all have our favorites, and if you can let us know what you're looking for, we'll all have suggestions.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry