It is I who am waiting for you.

"It's me" is how native speakers talk. But if we add a relative clause, I agree with Ben that "It is I who am waiting for you" is more probable in writing. But I already posted a longish answer on the other post that asks the same question. ;)

Adrian is right and wise.

Thank you Adrian!

Ben is correct, but if you say this in conversation, people will 'raise an eyebrow' because it sounds too formal. Most people would say 'It is me [OR ' It's me' ] waiting for you'.