I am definitely one of those guys that doesn't wear sandals or flip-flops in the city. I think it's just plain wrong. There are a few places where I deem it to be acceptable, namely beach cities, but then those are not really cities anyway. The likes of Rio, LA, Miami, Monte Carlo, Sydney, all have sun and heat in common, and, as such a sandal is just about passable if you are going to be near sand, boarding a boat or picnicking in a grassy park. In cities like London, Paris, or New York, urban metropolises, with pollution and traffic, millions of people trodding down the pavements, sandals and flip-flops lead to one thing alone. Dirty feet.
This said, I do think men should have a few pairs of either sandals or flip-flops which they can wear in the appropriate situations.
You should certainly have a pair of Havaianas, quintessential rubber Brazilian flip-flops that can be dressy or casual, they come in an array of colors, although my preference has always been with blue or green and never white, and they can easily be packed no matter how small your luggage allowance. I think its also acceptable for a man to have a pair of leather flip-flops if you are going for that linen trousers and polo shirt look by the dock and want to show a little more flair than a simple rubber option. Banana Republic have always had nice options for these and Prada as well. As long as you stay well and far away from Abercrombie and Fitch you will do fine. Dressier flip-flops can also look nice with an untucked shirt and some cleanly pressed shorts or a rolled up trousers and t-shirt for that I-just-threw-this-together look.
Recently 'Jesus Sandals' and 'Gladiator Sandals' have made an appearance in the men’s footwear market. While fashion-types seem to be enamoured with this style of footwear, its not as easy to wear as you think. It is true that it can go nicely with both trousers or shorts but the risk always remains of looking too fem even on the butchest of men. Looking on thecorner.com recently I noticed some Neil Barret multi-strap sandals along side a pair of Givenchy 'X' crossed strap leather sandals. Both pairs are typical of the trends at the moment, but both pairs also lend to the feminine looking sandals for men. I much prefer a simple sandal, with one strap across the toes, and a strap around the Achilles tendon to hold the sandal in place. Think Mexico circa 1973, that's what I'm picturing. Its classic, unfussy and not pretentious.
Who makes these specific sandals? Lanvin of course. In rubber and suede. You also have less chance for rubbing in various places along your feet. The important thing about sandals is to frame your feet nicely. They should compliment your foot and not make it look worse than it already may be. Sporty sandals like Teva or Chaco have their own place too but I would not include them in what I term stylish footwear, they are more purpose-built footwear. If I were to try my feet at sandal wearing, I would go with a pair of Acne Tour Low sandals in black leather. Simple and uncomplicated they seem to have some sort of ankle support and of course are Acne, so already they assume a cooler rating than most others. Topman, purveyor of all things fashion and even the odd fashion faux-pas, also have quite a wide selection of sandals which I don't immediately find offensive.
As long as you maintain some sort of sense of your masculine self, keep the sandals simple and avoid sandals which your mother or girlfriend might wear too, I don't think you can go too wrong. My last rule and piece of advice I can impart, is that you always avoid any sandals which are reminiscent of a Dictator of some small war-torn country in Africa. Those are not the sandals you should be wearing!