Web site and technology
I love how CO has embraced technology.
They have one of the finest websites and pda sites in the industry and they only get better. They continue to improve, and they routinely implement user/customer suggestions.
Paperless boarding continues to be another great example of embracing modern technologies.
Their commitment to LiveTV and in-flight internet domestically are further testament to this. Granted, they may not be the first, but I think they're headed in the right direction to be the best.