IshiHime because opposites attract and they are so cute and funny together.
IchiRuki because they are such a dynamic team.
GinRan because... he's hot and she's hot and there's grown-up drama there. Weee!
RenRuki because, honestly, he just loves her so much, and it's just an interesting dynamic
Urahara and Yoruichi--woah, the cat and the hat, baby. These are a sexy couple.
Yoruichi/Soi Fong--even sexier!
And I've got one crack pairing fave: KENPACHI AND UNOHANA! Yes, once that got into my brain, I haven't been able to get it out. Fanfics are starting to jump on that wagon and I think it's a pairing with lots of potential! He needs to be tamed; she needs to get WILD.