Coffee and tea, traditionally served hot, are also great cold.
Are there any drinks traditionally served cold that are good hot?
(And no, “iced coffee” and “iced tea” don’t count, wiseguy)
Lemonade!
Cider is good either way.
My parents used to bring Tang on camping trips to drink hot in the morning. I don’t know if it can be called “good” but it’s as least as good hot as it is cold. 
Is hot chocolate basically just chocolate milk that kids love, only, y’know, hot?
Rum punch.
Mulled wine. (Does it still count if the hot version has a few added spices?)
It is if you buy it from a coffee shop. Dutch Bros. and Starbucks both just heat up chocolate milk, and it’s gross unless you hide the flavor with a Torani syrup. (Almond coconut is nice as is orange. )
Mio Energy if you’re looking for a little caffeinated juice in the morning. Just pick one that is supposed to taste like fruit, and “green” is not a fruit.
My parents told me that, at least here in the South, in the 1940s-50s, Dr. Pepper warmed up in a pan on the stove was a thing. I’ve never tried it.
I once forgot a partial Dr Pepper in my car during a summer day at work, was really thirsty after a long day on the job. It was actually pretty good.
Was probably good that it wasn’t a completely full bottle or it likely would have made a huge mess.
Apple and cranberry juice
Whiskey
Hot toddies, but yes.
When I was a kid, Dr. Pepper ran a television commercial that encouraged this as a cold-weather treat. I badgered my mom into heating some up, and it was pretty good. (This was in the mid-60s, I believe.)
I remember it’s being advertised hot with a slice of lemon.
In the Detroit area, Vernor’s used to be heated and drunk in cold weather, or to cure what ailed you. It was pretty good, but I wouldn’t say it compared to the regular cold stuff.
Indeed! Though I think hot lemonade works better with honey as a sweetener than with sugar - wonder if that would work cold. Has anyone tried?
Warm Vernors (no apostrophe in the name) is wonderful. Not the same as cold, but equally good IMHO
Agua de jamaica is normally served cold, but I make it at home sometimes in the winter from scratch with added spices (cinnamon stick, ginger, allspice) and it’s awesome served hot.