I agree with Timmsp, the new Sun Country is great, but the old scheme is horrible. I spent the day at PHX, so I will say America West, US Airways, and Southwest(blue). The brown Southwest looks like a flying terd, great airline though.
My favorite is Deltaflot of course...although...it would be awesome if they interchanged the color of the fuselage with the light blue, white, dark blue, and red. I don't know how much more this would cost, but it really would look awesome. I also like United's and Virgin Atlantic's (new) schemes.
I recently had a chance to fly HP (MSP-LAS-SJC-LAS-MSP) and I agree that the new colors are 10 times better than the old scheme. The green is a great shade and the silver squiggles are a nice touch. I also admit that the A320 on one of the segments had about the nicest interior color scheme I've seen in a long time. The light blue seat covers made the cabin seem a lot lighter and roomier than other A320's I've been on.