9. CALLIE + MARK (Season 4)
What happens when Callie isn't sure she wants to go the same-sex route? Two words: sexual marathon. Hey-o!
Credit: Vivian Zink/ABC via Getty Images Photo: Derek and Meredith Have a Moment in Grey's Anatomy Season 3, Episode 2, "I Am a Tree"

What a tangled sexual web Grey's Anatomy weaves. Trying to remember who slept with whom can often be a taxing task. But there's no forgetting the moments below, thanks to their total hotness — and, sometimes, their total ridiculousness.

10. MARK + LEXIE (Season 5)

Remember when Lexie went over to Mark's place and told him that she respects him as a man and as a surgeon? And then she was all like, "Teach me. Teach me. Teach me. Teach me. Teach me. Teach me. Teach me." Yeah, kinda annoying. But also kinda hot, considering she went from knocking on his door to knocking boots in about 30 seconds flat.

1. MEREDITH + DEREK (Season 2)
So Meredith is dancing with Finn at the prom, and Derek is dancing with Addison. But of course Meredith and Derek are watching each other like hawks while telepathically conveying their desire to do the nasty with each other. After some pointless bickering, they do it — in slow-mo, natch. And then Derek's all, "What does this mean?" and Meredith is like, "Dammit, man, help me find my undies!" And then Callie walks in and gives Derek a great judge-y look. All in all, it's a pretty sensual scene. But don't they know that the teens are supposed to be the ones having sex at the prom?
2. CRISTINA + BURKE (Season 1)
Cristina walks into the on-call room, finds Burke shirtless, and says, "Thanks for the coffee" — obviously code for "DO ME. RIGHT. NOW." Burke strides over all cool and such, grabs Cristina's face, and they get ready to make some serious whoopee. The camera tactfully goes blurry.

4. CALLIE + ERICA (Season 4)
When Callie finally gets her ducks in a row, she finds Erica in the parking lot, prattling on about lost keys. Callie gets Erica’s attention by announcing, "I'm saying something." Then she lets her lips do the talking by planting a big wet one on Erica.

3. IZZIE + ALEX (Season 2)
When the hospital has that bomb scare, Alex likens it to an apocalypse. The real bomb drops when Izzie takes him to the on-call room and gets all up in his grill, saying, "I haven't had sex in 8 months and 12 days. I'm horny, I'm half-naked, and I'm saying yes. Do you want to stand there and talk metaphors or do you want to literally take off your pants?" And Alex does as he's told. Ka-BOOM!

5. OWEN + CRISTINA (Season 5)
Owen takes Cristina to a deserted part of the hospital, and she goes along despite the serious serial-killer vibes. He positions her on top of a vent, and all of a sudden a rush of air comes up from below. Cristina starts giggling hysterically, probably because that hot air is up in her lady business. Owen gets all heady, saying that they're "out of time, out of space" and that "anything can happen on the vent." In this instance, "anything" means a very hot make-out sesh.

8. MEREDITH + DEREK (Season 4)

Isn't break-up sex like having your cake and eating it, too? Oh well — it was still hot when Meredith and Derek did it, but it would have been more so if they hadn't kept chanting "break-up sex" like a self-affirming mantra.

7. BAILEY + BEN (Season 6)
Finally, Bailey gets some nookie! But first she has the requisite freakout after Callie grills her about lady-scaping, condoms, and other important matters. Little does Bailey know how much of a stand-up guy Ben is — he doesn't even need sex until the next date.

6. ALEX + ADDISON (Season 3)

After witnessing some serious eye contact going on between Addison and Alex, Callie accuses Addison of looking at Alex like a bear looks at a cooked turkey. (Remember Callie's "lines of deliciousness" line? Classic!) Addison claims she won't be sleeping with "the help," but she does indeed sleep with "the help" after a particularly heated argument with said "help." Oops!