I feel like I am on a roll with H&M this morning.....having already recommended them on another thread minutes ago!
But, for simple jersey dresses I think Hennes is fab. Some of their jersey dresses can be quite flimsy but their heavier jersey washes & wears beautifully. I have a teal dress (empire line, cross-over bust) which was about £15. Always gets compliments and has been worn over and over again.
They have them again this year - teal, plum, black and poss navy.