Fleur Delacour: Fleur is the Triwizard Champion from Beauxbatons, the French wizarding school.  She is part veela and she has long silvery blonde hair and blue eyes.  She flirts with Cedric sometimes, but I have a feeling she probably flirts with anything that moves.  Besides, if you were Fleur, wouldn't you flirt with him too knowing that, being part veela, you'd have a better chance?

Viktor Krum: I wasn't sure whether to put him under Friends or Foes, seeing that they're rivals in the Triwizard Tournament, but since Krum says at the end that he liked Cedric and that he was always polite to him even though they were rivals, Krum is in the Friends section.  Krum is a famous Quidditch player (he plays Seeker on the Bulgaria team) and he is the champion from Durmstrang.

Harry Potter: I consider them friends because they help each other out throughout the tournament.  Harry finds out about the dragons and so do Madame Maxime and Karkaroff, so he figures that Cedric is the only champion who doesn't know what the first task is and he tells him about the dragons.  Then Cedric gives him a hint (albeit a rather vague hint) about the second task, which Harry figures out even though it was kind of cryptic.  In the maze, Harry Stuns Krum when he, under the Imperius Curse, uses the Cruciatus Curse on Cedric.  Later they work together to defeat the spider at the end of the maze.  Because Harry has helped him so much, Cedric initially refuses to take the Triwizard Cup.  But Harry insists that they both take it at once so it can be a draw.
 
the other Hufflepuffs: well, obviously they'd support their own champion.  They don't seem to like Harry after his name comes out of the Goblet of Fire, because they think he's stealing Cedric's glory (Cedric doesn't seem to think so himself).  They all go around wearing those badges that say "Support Cedric Diggory" and flash "POTTER STINKS" when you press them, until Cedric tells them to stop, out of gratitude to Harry for telling him about the dragons.

Family
Amos Diggory: Cedric's father, who likes to brag about him a lot. ^^;; When he and Cedric meet the Weasleys and Harry on the way to the Quidditch World Cup, Amos won't shut up about how Cedric's team once beat Harry's team at Quidditch.  Amos also works for the Ministry of Magic at the Department for the Regulation and Control of Magical Creatures.  Although I bet in Book V he quits the Ministry, know why?  I heard somewhere (just a rumor, but I think this is plausible) that some members of the Ministry of Magic quit because of Fudge's refusal to believe that Lord Voldemort is back.  I can just imagine Amos Diggory saying to Fudge as he leaves the Ministry: "If Voldemort isn't back, then who do you think killed my son?"  Cedric's mother appears towards the end of the book, although her name wasn't mentioned (just Mrs. Diggory).  She and Amos meet with Harry so that he can tell them how Cedric died, and Harry offers them the gold that he won in the tournament, but she refuses.  As far as I know Cedric doesn't have any siblings, at least none have been mentioned, but wouldn't it be cool if he had a younger brother or sister who was starting at Hogwarts in Book V?

Foes
Lord Voldemort: Well, obviously, who _isn't_ Voldemort's foe?  Cedric especially because Voldemort was the one who ordered Pettigrew to kill him.  He didn't really have to, he just saw that an extra person had been transported with Harry Potter and he considered this person to be expendable, so he had Pettigrew kill him (I'm restraining myself very much to not start cursing at Voldemort right now... ^^;;;)

Peter Pettigrew: Also known as Wormtail, he is an Animagus (can turn into a rat, how appropriate) and one of Voldemort's most faithful followers.  He killed Cedric with Voldemort's wand (having no wand himself, having left it behind when he escaped from the scene of a mass murder and framed Sirius Black for it).
 
Draco Malfoy, Crabbe, and Goyle: Well, I don't think Draco was too sympathetic about Cedric's death, seeing as he was whispering to Crabbe and Goyle during Dumbledore's speech, and his remarks on the Hogwarts Express about "Muggle-lovers and Mudbloods first!  Well, second...Diggory was first."  Although they did wear the "Support Cedric" badges, I think that was just so they could flash "POTTER STINKS" at Harry at every opportunity.