Singapore is not shown, but is near the top, (150 countries vs Denmark's 157) and deserves special mention as the only passport that's visa-free for both US and China.
As an American in China, you have no idea how many times I've envied the Singaporeans. China goes out of its way to gouge Americans for visas - a visa costs about $150 for us, maybe $30 for a Canadian or European.
I'm told visas are about equally expensive for Chinese entering the US (although the US does a much more thorough background check to ensure the Chinese person has consistently had a good job with regular income), so I guess the feeling between the 2 governments is mutual.
The visas for foreigners here are also of relatively low quality - they have a short duration. And the rules about what a person can obtain are constantly changing. I've spent so much time, effort, and money dealing with visa issues, I've really contemplated marrying my Chinese girlfriend. We're not really ready to get married from a relationship perspective, but we're both pragmatists and it would save us money and headaches.
Yeah, tell me about it. I spent a small fortune on my multiple entry L visa in HK, and it was only good for a month at a time-- not quite enough time to get my long term residence visa. Worse yet, getting a simple extension while the paperwork goes through is more expensive than just hopping on a train and leaving the country only to re-enter it again. What a waste of my time, of space on the train and of fuel. And for what?
http://www.henleyglobal.com/citizenship/visa-restrictions/