Are, in no particular order:
Girls Just Wanna Have Fun by Cyndi Lauper
99 Red Balloons (the german version) by Some German Lady
Too Sexy by Right Said Fred
Hey Ya! by Outkast
Beat It by Michael Jackson.
Whatchoo got?
Try to stay in pure pop, no rock songs, jazz songs or straight-up hip hop.
Walking in Memphis by Mark Cohn
Sweet Dreams by Eurythmics
Smells Like Teen Spirit by Nirvana
Maryjane’s last Dance by Tom Petty
Word Up by Cameo
I don’t know about top five, but THE BEST pop song since 1980 is The Mayor of Simpleton by XTC, off their 1989 album, Oranges & Lemons.
(What’s So Funny 'Bout) Peace, Love and Understanding by Nick Lowe as performed by Elvis Costello & The Attractions is also up there, but misses the cutoff date by a year or so.
And by pop song you mean a song of roughly three minutes in length with a catchy hook and a definite, danceable beat, right, and not just some song that’s popular?
Yeah, pretty much. I was trying to exclude something like “Smells Like Teen Spirit” but let’s not be too picky. It’s definitely straddling the pop/rock line.
That’ll be 99 Luftballoons by Nena, just so you know. And I’d certainly agree on that one, I love that song.
Can’t really leave “Beat It” off of a post-1980 Top 5.
Neither can you leave off Prince. Here’s my not-too-mulled-over list (no order):
“Beat It” by Michael Jackson
“Let’s Go Crazy” by Prince
“You Spin Me Round” by Dead or Alive
“Bette Davis Eyes” by Kim Carnes
“Drive” by the Cars
Honorable mentions:
“Down Under” by Men at Work
“Obsession” by Animotion
“Don’t You Want Me?” by the Human League
“Crazy” by Seal
“When Doves Cry” by Prince
“One Headlight” by the Wallflowers
“The Way” by Fastball
“Whip It” by Devo
Tainted Love by Soft Cell needs to be in there somewhere, IMHO.
I would have gone with Little Red Corvette for a Prince song.
As a matter of fact, hearing it in the car the other day got wondering what the best pop songs ever are.
Yeah, Prince has a bunch that could be legitimately argued for top 5. Besides those we’ve named, you could go with “1999”, “Purple Rain”, “Sign of the Times”, “Kiss”, etc.
Steppin’ Out, by Joe Jackson
The Way It Is, by Bruce Hornsby
Avalon, by Roxy Music
Everybody Wants to Rule the World, by Tears for Fears
Livin’ La Vida Loca, by Ricky Martin (scorn all you want, but it is the perfect pop song and has to be mentioned)
Some very good suggestions here. If I could force myself to pick the 5 absolute best, some or all of my choices would be among those already named. However, also worth considering are…
Our House by Madness
Take On Me by a-ha
Come Dancing by The Kinks
Walk Like an Egyptian by The Bangles
New Song by Howard Jones
Off the top of my head, with an attempt to get some that haven’t already been mentioned:
Common People by Pulp
Girlfriend by Matthew Sweet
This Charming Man by The Smiths
Take Me Out by Franz Ferdinand
Blue Monday by New Order
Blister in the Sun by Violent Femmes
I put six in case one gets disqualified for not being pop enough. 
My early 80’s nominee would be Melt With You by Modern English.
My favorites:
There Is a Light That Never Goes Out - The Smiths
Fake Plastic Trees - Radiohead
A Question of Lust - Depeche Mode
Fall On Me - REM
True Faith - New Order
I’m also surprised that no one’s mentioned:
Forever Young - Alphaville
Not going to wrack my brain with trying to narrow it down to five, but I will mention the song I actually paid to get as a cell ringtone:
Men Without Hats “Safety Dance”
And as much as I have to say its pretty nearly my least favorite Counting Crows song, “Mr Jones” is a pretty perfect pop song.
1999, Prince.
Rock the Casbah, The Clash.
Walking on Sunshine, Katrina and the Waves.
Love Shack, The B-52’s.
April Fool, Rufus Wainwright.
And bubbling up this week to the Top Ten . . .
Sowing the Seeds of Love, Tears for Fears.
Forever Man, Eric Clapton.
Hole Hearted, Extreme.
Smells Like Teen Spirit, Nirvana.
Ray of Light, Madonna.
Another five not mentioned:
Groove is in the Heart Dee-Lite
Just Like Heaven The Cure
Fake Plastic Trees Radiohead
Milkshake Kelis
and, of course, how can we leave out:
Bizarre Love Triangle New Order
Oh, my Radiohead has already been mentioned. So let’s try, instead:
[bGirls & Boys** Blur
I chose mine based on appealing melody w/memorable hook, expression of Universal Truths in lyrics, and mass appeal. Extra points for creating a cultural niche.
Don’t Tell Me, Madonna
Come To My Window, Melissa Etheridge
Shape Of My Heart, Sting
Thriller, Michael Jackson
Falling For The First Time, Barenaked Ladies
Honourable mentions:
Short Skirt, Long Jacket, Cake
Free Fallin’, Tom Petty
Sweet Dreams, Eurythmics
Birmingham, Amanda Marshall
Tainted Love, Soft Cell
In my mind, the most perfect pop song of all-time is still “Enjoy the Silence” by Depeche Mode. Fantastic song.