Good question. I myself was a top-40 on-air personality for over three years.

Just to give you an idea of how complex the answer is to your question, here are TOPS OF the the current (as of this writing) charts from Billboard Magazine--if they're on there, they're contemporary. Define it as getting a lot of play on the air--Bon Jovi's stuff playing in Germany is likely from the late 80s to early 90s.

* Hot 100
November 20, 2010
What's My Name?
Rihanna Featuring Drake

* Billboard 200
November 20, 2010
Speak Now
Taylor Swift

* Radio Songs
November 20, 2010
Just The Way You Are
Bruno Mars

* Digital Songs
November 20, 2010
What's My Name?
Rihanna Featuring Drake

* Digital Albums
November 20, 2010
Speak Now
Taylor Swift

* Ringtones
November 20, 2010
Just A Dream
Nelly

Breaking & Entering
Number 1 Top

* Heatseekers Songs
November 20, 2010
All I Want Is You
Miguel Featuring J. Cole

* Heatseekers Albums
November 20, 2010
Habits
Neon Trees

Genres
Number 1 Top

* Pop Songs
November 20, 2010
Just A Dream
Nelly

* Adult Contemporary
November 20, 2010
Breakeven
The Script

* Adult Pop Songs
November 20, 2010
Teenage Dream
Katy Perry

* Dance/Club Play Songs
November 20, 2010
Hands
The Ting Tings

* Dance/Electronic Albums
November 20, 2010
The Fame
Lady Gaga

* R&B/Hip-Hop Songs
November 20, 2010
Can't Be Friends
Trey Songz

* R&B/Hip-Hop Albums
November 20, 2010
Merry Christmas II You
Mariah Carey

* Rap Songs
November 20, 2010
Right Above It
Lil Wayne Featuring Drake

* Rap Albums
November 20, 2010
I Am Not A Human Being
Lil Wayne

* Rock Songs
November 20, 2010
Say You'll Haunt Me
Stone Sour

* Rock Albums
November 20, 2010
Come Around Sundown
Kings Of Leon

* Alternative Songs
November 20, 2010
Tighten Up
The Black Keys

* Alternative Albums
November 20, 2010
Come Around Sundown
Kings Of Leon

* Hard Rock Albums
November 20, 2010
Escape The Fate
Escape The Fate

* Folk Albums
November 20, 2010
Sigh No More
Mumford & Sons

* Country Songs
November 20, 2010
As She's Walking Away
Zac Brown Band Featuring Alan Jackso...

* Country Albums
November 20, 2010
Speak Now
Taylor Swift

* Bluegrass Albums
November 20, 2010
Up On The Ridge
Dierks Bentley

* Jazz Songs
November 20, 2010
Put The Top Down
Dave Koz Featuring Lee Ritenour
*
Jazz Albums

November 20, 2010
Hollywood: The Deluxe (EP)
Michael Buble

* Blues Albums
November 20, 2010
Living Proof
Living Proof
Buddy Guy

*
Classical Albums

November 20, 2010

The 99 Darkest Pieces of Class...
Various Artists

* Latin Songs
November 20, 2010
Danza Kuduro
Don Omar & Lucenzo

* Latin Albums
November 20, 2010
Sale El Sol
Shakira

* Regional Mexican Songs
November 20, 2010
Nina De Mi Corazon
La Arrolladora Banda el Limon de...

* Regional Mexican Albums
November 20, 2010
El Hombre Que Mas Te Amo
Vicente Fernandez

* Latin Pop Songs
November 20, 2010
Danza Kuduro
Don Omar & Lucenzo

* Latin Pop Albums
November 20, 2010
Sale El Sol
Shakira

* Tropical Songs
November 20, 2010
Danza Kuduro
Don Omar & Lucenzo

* Tropical Albums
November 20, 2010
Prince Royce
Prince Royce

*
Christian Songs
November 20, 2010
Starry Night
Chris August

* Christian Albums
November 20, 2010
WOW Hits 2011
Various Artists

* Gospel Songs
November 20, 2010
I Believe
James Fortune & FIYA Featuring Zacar...

* Gospel Albums
November 20, 2010
Rehab
LeCrae

* Independent Albums
November 20, 2010
My Kinda Party
Jason Aldean

* Catalog Albums
November 20, 2010
The Taylor Swift Holiday Collection (EP)
Taylor Swift

* Holiday Albums
November 20, 2010
Merry Christmas II You
Mariah Carey

* Reggae Albums
November 20, 2010
Distant Relatives
Nas & Damian Marley

* World Albums
November 20, 2010
Christmas
Celtic Thunder

* New Age Albums
November 20, 2010
The Very Best Of Enya
Enya

* Comedy Albums
November 20, 2010
Words Words Words
Bo Burnham

* Kids Albums
November 20, 2010
Hannah Montana Forever
TV Soundtrack

* Soundtracks
November 20, 2010
Hannah Montana Forever
Soundtrack

* Tastemaker Albums
November 20, 2010
Escape The Fate
Escape The Fate

International
Number 1 Top

* European Hot 100
November 20, 2010
Only Girl (In The World)
Rihanna

* European Albums
November 20, 2010
Greatest Hits - The Ultimate...
Bon Jovi

* Japan Hot 100
November 20, 2010
Beginner
AKB48

* United Kingdom Songs
November 20, 2010
ONLY GIRL (IN THE WORLD)
RIHANNA

* United Kingdom Albums
November 20, 2010
MESSY LITTLE RAINDROPS
CHERYL COLE

* Germany Songs
November 20, 2010
ISRAEL KAMAKAWIWO'OLE
OVER THE RAINBOW

* Germany Albums
November 20, 2010
SCHWERELOS
ANDREA BERG

* France Songs
November 20, 2010
MIGNON MIGNON
RENE LA TAUPE

* France Albums
November 20, 2010
SALE EL SOL/SUN COMES OUT
SHAKIRA

* Canadian Hot 100
November 20, 2010
Only Girl (In The World)
Rihanna

* Canadian Albums
November 20, 2010
Speak Now
Taylor Swift

Web
Number 1 Top

* iLike Libraries: Most Added
November 20, 2010
Just The Way You Are
Bruno Mars

* iLike Profiles: Most Added
November 20, 2010
Just The Way You Are
Bruno Mars

* AOL Video
November 20, 2010
Hidden Away
Josh Groban

* AOL Radio
November 20, 2010
DJ Got Us Fallin' In Love
Usher Featuring Pitbull

* Yahoo Video
November 20, 2010
Love The Way You Lie
Eminem Featuring Rihanna

* Yahoo Audio
November 20, 2010
Mine
Taylor Swift

* MySpace Songs
November 20, 2010
Right Above It
Lil Wayne Featuring Drake

And then you've got Billboard's
* Eventful: Most Demanded Performers
* Eventful: Today's Hottest Demands