I don't know if this counts, but Patrick Stewart voiced Lord Yupa
It does count, in my opinion, since Nausicäa was a Miyazaki film.
Sad part about this list is, this isn't even half of the stars. Princess Mononoke alone was an all star cast. Spirited Away had more than a handful there as well. This list should be much much longer. I am very disappointed in it.
Steamboy wasn't a Ghibli movie
Also, in princess mononoke, Billy bob Thornton is Jiko
Also Phill Hartman's last role was the cat Jiji from Kiki's Delivery Service
Ummm.... Pod was voiced by Will Arnett
Mark Hamill was the villain in Castle in the sky
Tina Fey was Lisa in Ponyo
They are missing a lot of people..
Mark Strong as Pod was only in the UK release of Arrietty (which was a completely different cast and also kept the original music, unlike Disney's US release.).