Dislikes Intensely:
Regulus Black (although he would be moved to the "Loathes" category if Severus knew he's responsible for sabotaging Remus' motorbike)
Neville Longbottom
Harry Potter
Kingsley Shacklebolt
Bill Weasley (although he would be moved to the "Loathes" category if Severus knew he pushed Remus down the steps in front of Gringott's)
Molly Weasley

Family:
The Bump aka The Hairball (child, gender unknown, carried by Severus)
Cymbeline (daughter, carried by Remus)
Gaewyn (pet dragon)
Remus Lupin (spouse)
Serenus Snape (twin brother)
Winslow (pet Criffler)

Severus and Serenus' mother died under suspicious circumstances when they were 13; Severus believes his father is responsible for her death. Their father is still alive, but Severus hasn't seen or spoken to him in 25 years or so; he doesn't know about Serenus. Their mother's name was Megaera, and they had two aunts on their mother's side, Alecto (who raised Serenus) and Tisiphone (fate unknown). Severus inherited the run-down Snape estate from a distant relative from the main branch of the Snape family named Aloysius Snape; his father was overlooked due to Aloysius' approval of Severus' (apparent) support of Voldemort.

Friends:
(aka people he actually likes as opposed to merely tolerates)
Noah Jackson
Draco Malfoy
Charlie Weasley
Percy Weasley
Blaise Zabini

Loathes With the Searing Heat of a Thousand Suns:
Sirius Black
Lucius Malfoy

Lovers:
Regulus Black (although Severus doesn't remember their one-time encounter back in 1980 before Regulus faked his death, due to being Obliviated)
Remus Lupin (current relationship. First time here)
Draco Malfoy (once, here)
Lucius Malfoy (past relationship; Severus was involved with Lucius during his late teens until Lucius dumped him to marry Narcissa)
Serenus Snape (once, here)
Nymphadora Tonks (once, here)
Percy Weasley (once, here)
Blaise Zabini (once, here)

The only characters I can't really categorize are Tonks, whom he's annoyed by, but not enough to put her on the "Dislikes Intensely" list, and Millicent, with whom he has the Bill/Tonks problem (i.e. they have tremendous difficulty in communicating with and understanding each other), although he doesn't dislike her. Everyone else, he pretty much doesn't care about one way or the other, and if he relates to them, it's with annoyance and/or impatient disdain.