I've compiled my own lists (I have no life, ha!). They contain some names that have already been mentioned.
Men
Brad Pitt - I've just never seen the attraction.
Justin Timberlake - Makes my skin crawl.
Vince Vaughn - You know how sometimes you develop a irrational hatred for someone you've never met? VV is my target. An unfunny, weasel-faced ratfink. I'd rather have head lice than spend ten minutes with him.
Jude Law - The plastic man. There's something so superfical about him.
Matthew McConaughey - He's such a poser. Everytime I see him in that D&G ad, I want to puke.
David Beckham - Not attractive at all. A man with very little real backbone and an even lesser intellect.
Zac Efron - Looks like a ladyboy. Make your mind up, Zac - do want to be a man or a woman?
Tom Cruise - Even when younger, I've never considered him attractive. He always has that fake smile plastered all over his insincere face.
Charlie Sheen - Have never thought of him as appealing. Now that he's starting to look even rougher (say NO to drugs, kids!), he's trying to present himself as a charming older Lothario. It's not working, Charlie.
Keanu Reeves - A drainpipe of a man. Has about as much personality as a drainpipe too.
Colin Farrell - He's OK looking, but what I find off-putting is his own obvious belief that all women should worship him. He also tries so hard to shock by swearing on TV, smoking and drinking to excess etc. and then acts all casual about it. We get it, you're a bad boy. An overrated bad boy.
Women
Victoria Beckham - With those sunken cheeks, piggy nose and perma-pout, this stick-insect is visually offensive. She has no genuine talent and lives off of the success of her vapid husband. Oh, and she's supposedly a fashion icon...at least, she thinks she is. Her kids are merely accessories to her.
Paris Hilton - Ewwww! It's that long nose. Somewhere an anteater is looking for that.
Sarah Jessica Parker - To quote Peter Griffin in Family Guy: "Her face looks like a foot."
Cameron Diaz - Why do people think she's so beautiful? She has weird tiny eyes and a horribly wide mouth.
Madonna - Was once attractive but has now gone out of her way to become a man. Those muscles are too much and her face is so harsh now.
Tara Reid - I could go for the jugular and attack her unfortunate surgical procedures, but I'm not going to sink that low. Her face is rather boring - bland, even. I'd rather stare at a blank piece of paper.
Pamela Anderson - I'm sure you've all seen the pictures of her without her usual bucket-load of make-up on. 'Nuff said.
Denise Richards - She's not unattractive, but there's something about her that disturbs me. It might be the fact that her face still looks like a child's while her body is definitely that of a grown woman.
Jordan/Katie Price - Famous because of her hugely inflated chest. Always has waaaaaay too much make-up on, and when she takes it off, it's like looking at a different, even less attractive person. She has no class whatsoever.
Jodie Marsh - The exact same reason as above.
The Olsen twins - They look like Gremlins. Pure and simple.
Wow. I didn't realise that I had so much venom stored up in me. Ladies, I thank you for the catharsis.