The Alternative Guide to the City of Doors, by CrimsonLotus over on Planewalker, is one of my favouritest things ever.
Moradin's Festhall (big gay dwarven rave/fight/orgy) and Labrys Foundry (a lesbian Fire-Elemental nightclub/body art parlour, packed with Fire Genasi, Tieflings, and many other bashers with Fire Resistance) are now definitely included in my Planescape games. Each is dripping with plothooks and flavour, and could be the focus of little mini-campaigns themselves!
It's a look at something that doesn't get too much coverage in gaming - alternate sexuality. It makes sense that, in Sigil, sexual identity is near enough a non-issue (especially amongst the Anarchists, or Xaositects, and definitely the Sensates). With the amount of part-human/demihuman races (Half-Elves, Half-Orcs, Half-Giants, Half-Ogres, Half-Fiends, Half-Dragons, Genasi, Tieflings, Aasimar, Rilmani... the list goes on) one would be crazed to see such a surfeit of cross-species reproduction as less of an issue than same-sex relationships.
Perhaps some of the more militant Factions and religious peoples amongst Sigil's populace might find such things to be offensive, but I'd assume that, for the most part, people are fairly free to live their lives as they wish.
At least, they are in my Sigil.