Kali Mist is supposed to have that effect but not sure if the newer, slightly indica KM is that way. I think all weed helps with sex but I would like to find one that is tops at it.

FWIW, there's a little seedbank in holland that claims to have a strain that specifically enhances sex.

I emailed them and they claim in fact it does enhance sex but they didn't elaborate, so who knows.
Hemcy Seed Company

Check out Alpha Bud. I believe they ship to the US.