The Greek name for "machina" is μηχανή. It was used for more than just solving knots in a plot. In a way it was one of the earliest "special effects."

I'm not sure what Clouds reference prospero means, but when Socrates first appears, up in a basket examining the heavens, he is probably on a μηχανή. I suspect this is a deliberate allusion to sophists acting like gods. (I think it's rare to find anyone but gods on a μηχανή.)

Wikipedia thinks that in Aristophanes' Thesmophoriazousae (aka Thesmo), Euripides enters a scene on a μηχανή in comic allusion to his frequently resorting to it to solve plot problems [1]. I'm not sure what scene that is, but I'd encourage anyone to read this little-read play, in which Aristophanes stages Euripides trying to infiltrate a conclave of women upset that his plays show women in a bad light (e.g. Medea). During the play Euripides has to keep acting out scenes from his own plays. If you like Euripides, it's a pretty great read.

[1] http://en.wikipedia.org/wiki/Deus_ex_machina

I didn't know about the latter example, though, thanks for tracking that all down.