Well, off the top of my head…
Ride the Pony
She’s Tight
both by Cheap Trick
Gee, I think nearly every song written by Rick Nielson references sex in some way. But those are my “favorites”.
“Doin It” - LL Cool J
Feelin’ Love Paula Cole
As mentioned by Sea Lemon, the winner absolutely has to be “Let’s Get it On” by Marvin Gaye.
“I Like my Baby’s Pudding” by Wynonie Harris
“Sixty Minute Man” by Billy Ward and the Dominoes
“Big Ten Inch”…damn, forgot his name
“Everybody’s Talkin’ About Sadie Green” by the Memphis Jug Band
Darlin’ Nikki by Prince
See you in the hotel lobby!
Ukulele Ike, I think Aerosmith did a cover of Big Ten Inch. Is that close enough? Is it even the same song?
Sexiest ever, ever, ever: “The Sensual World” by Kate Bush (mmmmm, yes)
-Anything and everything by Prince
-“Heaven in a Black Leather Jacket” by the Sixths (Stephin Merritt)
Hmph.
It figures that the first song that came to mind for me was:
I Touch Myself by the DiVinyls
I’ve been alone too long.
One of my favorites is a song that no one at all seems to realize is about sex:
“Chestnut Mare” by the Byrds
What do you think they meant by singing in the chorus “She’ll be just like a wife,” anyway? 
Seriously, the lyrics speak about landing right on top of her, riding her, seeing a snake standing up and ready to strike (now what can that represent?), flying (a fairly common metaphor), landing in a splash of water, and vowing to ride her again one day. If you think that’s just talking about a horse, you lead a very sheltered life.
Other favorites about the subject:
“Kama Sutra” by the Bonzo Dog Band
“Mr. Skin” by Spirit
“Let’s Do It” and “Let’s Misbehave” by Cole Porter
“Guys are Not Proud” by the Anemic Boyfriend
It’s been mentioned, but “Paradise by the Dashboard Light” is a true classic.
Eazy-E - Gimme Dat Nut
/old man voice on
Ah, you kids with your new fangled Nine Inch Nails and your crazy rap music don’t know nothin’. Ya got no imagination at all. I’m my day we had real sex songs…
/old man voice off
I submit:
Clarence Carter - Strokin’
Joe Cocker - You can leave your hat on
And who can forget:
Leon Redbone - Seduced
TMR, I’m with you though, Jimmy Buffet ‘Let’s get drunk’ is a classic.
I Want A Lover (Pet Shop Boys)
Bad Touch a.k.a. like the Discovery Channel (Bloodhound Gang)
back in the days of old time radio, often we would hear a song, June Is Busting Out All Over, which I remember was about the changing seasons rather than about a girl named June, but I also remember that Charlie McCarthy shared the more sexual interpretation of that title; I still laugh when I think of it.
to answer the question seriously:
Hungry Like The Wolf - Duran Duran
Thinking About Sex Again - The Waitresses
and following those,
Max Don’t Have Sex With Your Ex - ???
Well, in the playlist entitled ‘Make Out’ BunnyPapa and I have:
Rock Me Tonight - Billy Squier
Shakin’ - Eddie Money
Satisfaction Guaranteed - The Firm
Shake Me - Cinderella
I know there’s lots more, I just can’t think of them right now…
Uh, “Rosie” by Jackson Browne.
I totally agree with Lsura and struuter on this one!
I Wanna Sex You Up, Color Me Badd
Blue Light, Ho’onua
Freak Me, Silk
I Want You, Third Eye Blind
Slow Love, Doc Box and B. Fresh
Wild Thing, Tone Loc
Knockin’ Boots, Candyman
Let Me Love You Down, Ready for the World
Crash, Dave Matthews Band
I nominate “Turning Japanese,” which is about whacking off, by the best one-hit wonders ever, The Vapors.
I also seem to remember that Barnes and Barnes – they of “Fish Heads” fame – did a song which noted, “Wouldn’t it be so WON-derful if you were to touch yourself? I’d like to take a PHO-tograph of you as you touch yourself.”
And, yes, those DiVinyls …
I gotta back up Sixty Minute Man. That’s a fine song.
Do Ya Wanna Touch Me: Joan Jett
My baby rocks me with one steady roll: Big Mama Thorton
Reelin and Rockin: Chuck Berry
Kids today…jeez
Fuck like a Beast by WASP
Love me Like A Reptile by Motorhead (hell most of Motorhead is about sex)