Good question - that's why I like looking at the cabin photos at a.net so much.
Some that come to my mind:
LH - too much grey but the yellow accents are OK
BA - elegant and stylish
VS - outrageous!
AF, KL - nothing special
AZ - the green seats are a bit odd these days
SK - nice cabin accents of beige and red to the blue seats
EK - nice sandy desert colors
AC - nice combination of dark green, grey and maple leafs
new Southwest - just great!
Most First and Business cabins are more styled, so I'm talking about Economy here.
What I don't like so much is the standard blue seats and white walls/overheads.
Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been...