(In no particular order).

Remus Lupin: Milk tea. He keeps teabags with him since he travels a lot and they are convenient to use instead of brewing the tea all the way. Though earlier in his Hogwarts days, his most preferred drink used to be hot cocoa brewed especially by Sirius Black. Sirius had learnt how to brew cocoa and coffee by Mrs Potter and it became his specialty. He would treat his friends to cups of hot cocoa frequently. However, after James Potter's death and Sirius's imprisonment in Azkaban, Remus has not touched hot cocoa ever since.

Nymphadora Tonks: Mixture of various drinks, preferably self made cocktails. She likes to mix a lot of drinks together to create her own mixtures. She would try mixing Butterbeer and red currant wine, or Firewhiskey with Madam Puddifoot's coffee.

Sirius Black: Firewhiskey, obviously. He likes the burning sensation it gives on the insides and prefers it more than any other drink. But secretly, he also loved Lily's especially brewed coffee and Peter's recipe for orange cocktail.

Lily Evans: Coffee. Lily used to study a lot which kept her awake at nights and to get rid of sleepiness, she preferred to have a cup of black coffee with scarcely any milk in it. She was addicted to caffeine.

James Potter: Iced tea, preferably apple flavored or pear flavored. James liked to have cold drinks instead of hot and the hot cocoa made by Sirius was the only hot drink he ever touched.

Peter Pettigrew: Butterbeer. Peter was very simple and not really choosy with his drinks, he would gladly drink anything as long as it contained lots of sugar in it. He was much of a sweet tooth and preferred sweet sugary drinks.

Ginny Weasley: Cold coffee.

Luna Lovegood: Gillywater and anything as long as she gets to name the substance. Snapdragon Essence, Guillamore Nector and the list is never ceasing.

Arthur Weasley: if he ever tried the Muggle Starbucks, I'm pretty sure that would be his favorite.

Newt Scamander: freshly brewed tea with powdered cinnamon. He has been having this ever since he was a child and it has become a characteristic aspect of his personality.

Horace Slughorn: Mulled mead and any other alcoholIc bevarage Madam Rosmerta's inn has to offer.

Severus Snape: Even though he hates to admit it, Snape likes to have tea but he drinks it quite rarely since it reminds him of Mrs Evans and her wonderful tea when he first visited their house with his mother Eileen Prince.

Narcissa Malfoy: Earl Gray tea. She is the sort of person who likes to establish her status and personality in the minds of others by her preferences and actions alone. Narcissa prefers to drink this tea because not only it shows that she's British (well, you should know that Earl Gray is a drink specified to English people only) and that she has great taste in drinks and beverages as well. 

Draco Malfoy: Pumpkin Juice. I know it sounds weird but in the whole of the Hogwarts feast, the pumpkin juice was his favorite and basically the only thing which kept him coming to the table with his house mates for the feast. Other than that, he ABSOLUTELY LOATHED having to sit at the feast and watch the GRYFFINDORS and the others getting UNNECESSARILY cheery and merry.  

Lord Voldemort: a lot of drinks apparently and well, his preferences vary. Unicorn blood, Elixir of life, practically anything that could make him immortal and for the past few years... THE BLOOD OF THAT ABSOLUTE NUISANCE AND IRRITATING HARRY CHOSEN POTTER.  

These are not all of course, but only those I could think of. I might add a few if I get new ideas.

Upcoming Chapter: S.P.E.W