heheh, actually this time I'm like Bipa and didn't vote because my answer doesn't fit into the categories!
On the one hand, there is cutesy type dog clothing, such as this
http://www.thepuppyshop.com/apparel.html
This type of clothing may or may not be functional. Many of them are not, most are just for the amusement of us humans. But some of them are also functional (meaning that they do keep dogs warm on cold days), and I actually would LOVE to get my dog something like that because I think he would look cute in it as well. Well maybe not necessarily in a floral pattern but something cool looking. Unfortunately they don't seem to make a lot of cute-looking clothing for big dogs (mine is a german shepherd), such cutesy clothing seems to only be available for small dogs. maybe that's for the best..... Well my parents did get my dog a denim jacket that was also functional when he was a puppy, and he looked very stylish in it but then he outgrew it. Now the closest I've seen is an imitation air-force bomber jacket that is sized for big dogs. I was so tempted to get one for him, I still might...! (I'm generally not an impulse shopper except when it comes to my dog, which makes my husband roll his eyes, hehe!)
Then my dog does own a truly functional jacket, these types of jackets are no-frills, like the kind some hunting dogs wear, and look more like horse blankets in general (i.e. boring looking, and not cute). My dog has this one:
I make him wear it if we are on outdoor excursion in the winter and the temperature is lower than about 5 oF. He has a double coat, but dogs can still get cold if spending a lot of time outdoors in the winter especially if there is windchill. If the dog does not even have a double coat, like many of the short-haired breeds, then they actually DO need to wear coats in the winter if they doing outdoor activities. Examples of such breeds are greyhounds - I know several greyhound owners who exercise their dogs everyday year round, but greyhounds cannot handle even mild winter days outside naked because their coats are so thin, with them the rule of thumb is that if you need a jacket then so does the dog. in the winter I always see them wearing these types of jackets.
And then hunting dogs wear jackets that have bright reflective orange color, which I guess are for safety since they are around guns a lot!!
Then there are boots for dogs, like this.
These are also functional, again for winter if your dog is going on a long hike in the snow, because the snow could compact in between his toes and cause frostbite. I've seen sled dogs and skijoring dogs wearing these boots when working. Or, if hiking in very rough terrain where there are thorns or sharp rocks, these boots are also functional and practical and I've seen people hiking with their dogs in the rugged backcountry where their dogs were wearing these boots.
My dog doesn't have these boots, but I'm seriously considering them. There was one time when we were hiking in the rugged backcountry he wandered into a patch full of thorns and they got embedded in all of his paw pads at the same time, he didn't yelp, he just simply suddenly stopped walking and refused to move. When I went to remove the thorns they cut my hands quite badly. These thorns were not visible in the tall grass so I didn't see them ahead of time. thus now I would seriously consider making him wear these boots if we are in places where the terrain is very rough.
He really doesn't mind it, though. We don't go out late at night often, but I got him a reflective vest to make him more visible for when we do.
