Learning that my mother got her groove on to Nina Simone when she was a 20-something airline stewardess sort of spoils her for me. I can’t get that image out of my mind. 
Rock/Alternative Songs:
Cowboy Junkies - Blue Moon Revisited
Sinead O’Connor - I Want Your Hands on Me
Catherine Wheel - Black Metallic
Fiona Apple - Criminal
Kirsty MacColl - Walking Down Madison
Stone Roses - Ten Storey Love Song
R&B/Hip Hop Sings:
Fabolous ft. Tamia- Into You
Robin Thicke - Lost Without You
Groove Theory - Tell Me
Mario - Let Me Love You
Trey Songz - I Invented Sex
Method Man ft/Mary J. Blige - You’re All I Need
Ne-Yo - Part of the List
Nicki Minaj part of Young Money’s Bedrock
When I used to dj online, I had my ‘naughty’ set - the songs that used to make me feel horny when I was a teenager. For me, it was a combination of the music AND the music video.
Jump - Van Halen (DLR crawling along the floor towards the camera. Course now, not so much)
Need You Tonight - INXS (leather jacket on bare skin and that dance move)
Damn, Wish I Was Your Love - Sophie B. Hawkins (her hair splayed on the floor)
I Touch Myself - Divinyls (nothing to say, 'nuff said.)
I really like that song. There are two versions, I love the original.
Since you brought up modern R&B, I will add R Kelley. Not his nonsense operatic saga, but all of his other stuff, I like.
This song makes me want to lick my fingers and twist my nipples…
Glory Box by Portishead. Much like Massive Attack, most any of Portishead’s music could be considered fuck music.
From the way back machine, Mea Culpa by Enigma. There’s even a lot of heavy breathing over the bump and grind rhythm toward the end of the song.
White Stripes Ball & Biscuit gets to me every time
This guy I worked with (and totally wanted to nail) admitted to a coworker (in a conversation I overheard) that whenever he hears a woman sing “Me and Bobby McGee” it really turns him on. So the next time we hung out, I made sure it was at a bar with Karaoke… and you know what I did.
He later said he didn’t know why that song turned him on… it just did.
Got up when the song came on, started singing, sounded like a wounded sheep, sat back down so embarrassed you wished the ground would open and swallow you whole, transferred to another department? 
That’s a good one - nice, slow groove.
Same except I’ll add “Slow Like Honey.” Damn.
Um… the opposite… of all of it.
He turned into a psycho a few months later… he ended up being the one who left the company… Well, got fired because he’s a psycho…
I sure know how to pick 'em.
That’s the album I was going to mention. The album is atmospherically very dark (I describe it as sucking all the light out of a room), but damned if it’s not good fuck music.
And in college, for whatever reason, Enya seemed to have a knickers-dropping effect on women.
For me, it’s Buena. That opening bass line is so very sexy.
This is one of those fantastic songs where I don’t even really understand what he’s talking about, but I understand what he’s talking about. You know?
I’d say:
The Doors - Back Door Man
Gov’t Mule - Bad Little Doggie
Led Zeppelin - Custard Pie
Closer - NIN
Oh, yeah!
These, two!
Add me to Massive Attack’s Mezzanine fan club. I’ll never forget the first time I heard that album. It was almost like a religious experience.
Others:
“Since I’ve Been Loving You” by Led Zeppelin
“Lover, You Should Have Come Over” by Jeff Buckley
“The Rhythm of the Heat” by Peter Gabriel
Collide’s song Inside is pure sex.
So is Diana Krall – her renditions of Peel Me a Grape and Frim Fram Sauce are steamy as hell.
To mention something different, The Golden Palominos’ LP Pure is basically an album for shtupping. (You can tell that from the cover, with its closeup photo of a woman’s naked breast.) Standout tracks: “Anything,” “Pure,” and “Heaven”.
But my current fave groin-greaser is Jimi Hendrix-influenced Muse B-side “The Groove” [live, probably from '04], which true to its name has a really sexy groove that I’m confident will convert 99% of you into Muse fans if you give it a chance. This rarely-performed track clocks in here at a compact 2:33 and features one of Matt Bellamy’s better guitar solos, which is saying something (he’s got of a lot of good ones).