Boat Shoes

So called because the original point of these rubber-soled pieces of footwear was to give sailors better traction on the deck of dangerously swaying ships, boat shoes are a welcome addition to any landlubber's wardrobe this summer. Usually available in a variety of materials, canvas is definitely your best option to beat the heat (at least when your even more comfortable sandals can't be worn). And much like those always comfy sandals, you can feel free to wear these bad boys sans-sock to keep that pesky temperature down even more. They're available in a wide variety of colors so they're easy to match with any existing wardrobe items you might have your heart set on for the season. The full-on sailor look can be a little off-putting if not done right, though, so avoid mismatching these with white pants or buying pairs with too much ornamentation or extra laces; go with the simple comfortable ones, instead.
Loafers
Similar in design to the boat shoe (and with the bonus of sometimes having straps reminiscent of a pair of nice, trendy summer sandals), loafers have the added benefit of being even lighter than them - with any luck, you'll barely notice you have them on. They're a versatile shoe that combines well with almost anything, and the clever dresser will be able to match a good pair of loafers with both casual and formal outfits. Wear them with socks, or, if you're particularly daring, go for the Miami Vice look and avoid socks altogether - more power to you. As comfort goes, they're not quite as comfortable as sandals, but darn it, they come close; a well-chosen pair of loafers will walk you through any door.
Converse All Stars
Comfortable sandals may be the pinnacle of relaxed footwear in summer, but the evergreen "chucks" are a very close second, bringing to their wearers something that sandals, however easy on the foot, lack: the ability to run in them. Ever tried to play an impromptu summer game of basketball in sandals? It's a recipe for a fall and a subsequently broken nose. Much as we enjoy the relaxed comfort of sandals (and we do love a comfortable pair of sandals), we have to give credit where credit is due and name Chuck Taylors as the shoe that best combines comfort AND practicality for any casual summer occasion. Like some of the other styles we've listed here, they're made of tough but breathable cotton canvas and available in an overwhelming variety of colors in addition to being cheaply priced, so why stop at one pair? Get yourself a set of All Stars for all possible combinations.
Flip-Flops
The close cousin of the ever-comfortable sandal and possibly the only item of footwear more relaxed than they are. They'll make you more relaxed too, if only because a relaxed walk is about as fast as you'll ever be able to go in these; any faster and you'll leave them behind on the sidewalk and wonder why you left your poor, comfortable sandals at home. Flip-flops have long been relegated to the realms of beach culture and Australia, but as with many other unusual clothing styles, hipster fashion has seen them make a resounding comeback. Extremely cheap and available in a million different shapes, sizes, and colors, flip-flops are about as close you can get to walking around in bare feet while still being shod, and are thus an excellent choice for any casual situation. Be careful, though; when the sign says "No Shirt, No Shoes, No Service", they mean you, casual flip-flop wearer. Bet you wish you'd worn those sandals now, don't you?
Woven Slip-on Shoes
Similar to the loafer in appearance and manner of being put on, slip-ons will give a sophisticated and old-school summer look in those scorching temperatures when the more comfortable sandals just aren't an option. There's a huge number of different individual designs for this shoe, but they're all equally breezy and light, so pick out one pair for formal dress and another for more casual combinations when shoe shopping, perhaps one white and one black. One color you'll want to avoid with these shoes is brown, or at least the earthier variety of brown; because of their design, woven slip-ons in that color tend to look less like shoes and more like you stepped out of the house wearing the laundry hamper on your feet.