...Blarg, I will regret this and it will probably come to nothing but may as well lay my cards out just in case.  Considering a couple of things but um let's see...

First off, Ultimate Spider-woman, or as Gowi once called her "Ben Reilly with boobs".  Main problem here is that as a genderswapped clone of Spider-man there needs to be a Spider-man already around (not entirely picky as to which, so Peter, Miles or even Gwen could work (although in the latter case she'd end up just being a straight-up clone rather than genderswapped I guess)) and for him to have been operating for enough time to have clone shenanigans be a potential thing.  ...Basically I've always had this weird fascination with the Clone Saga due to it having some potentially good ideas that weren't pulled off so well but yeah. ^^;

Secondly, female Thor.  But with the twist that instead of "a woman finds Mjolnir and gains Thor's powers" like every version of a woman finding the hammer turns into it's instead "a woman finds Mjolnir and [i]turns into Thor[/i]".  Basically, it's a woman who transforms into Chris Hemsworth when she's superhero-ing. XD

Last idea was something involving the Fantastic Four (probably the most vanilla of my options here really) but that requires a lot of cooperation to get the entire team to work so hmmm.

[s]Or I could try and figure out a suitable Marvel character that I could muck about with so they basically become a Kamen Rider in all but name[/s] YOU SAW NOTHING.