I'm really liking knee-length cardigans these days. It feels more current than my mid-thigh boyfriend cardis, which I still wear also. Here's the thing, though: I don't always want to wear such a long cardigan. Often I just want a short topper to keep my arms warm, without covering up my whole outfit. For that purpose, I wear shrugs that I've made, or a more traditional cardigan like the Halogen 3/4 sleeved version below. It doesn't strike me as especially current, but I don't think it's out of style; it just seems a perennial classic. One I like even better--because it's shorter--is by Loft, in Finds. But so far they are not showing colors that I want at the moment. Another Loft one I liked, but not in colors I want, is the Ribbed Open Cardigan. Maybe I'll get it in the light gray, although that's not a particularly flattering color on me.
Oh, another one I just picked up this season and really like is by Nic & Zoe--the Four-Way Cardi.
Getting just the right cardigan for an outfit can be hard for me. I also wear jean jackets in summer to provide warmth in air conditioning.