Missy Elliot and M.I.A.

As for the rest, you don't hear from Queen Latifah, Lil Kim, Eve, Salt & Pepa, etc. anymore because they suck. All of them. None of them were ever any good. In fact, the only reason they ever got any airplay at all is BECAUSE they were female rappers. Latifah is the perfect example. MTV and the record companies tried to force her down people's throats with constant airplay and talk of how "revolutionary" she was, but no one with any sense ever liked her. Ever.

Missy Elliott and M.I.A. are the exceptions. They are both great, but a little avant-garde, which is why they never got truly huge.

Lauryn Hill is not a rapper. Just because she rapped a couple lyrics on Miseducation doesn't make her a rapper. Everything she's ever done is great, but she's not a rapper.

There's no mystery here. There just aren't enough female rappers who are any good.