Since there is upcoming movies on based on "Transformers", "He-Man", "Voltron", "Bucky O'Hare" and "G.I. Joe", there should be a possible Thundercats movie and if so, who would you cast?

Lion-O: Nicolas Cage.
Cheetara: Naomi Watts.
Panthro: Samuel L. Jackson.
Voice of Snarf: Seth Mcfarlane.
Tigra: Heath Ledger or Matt Damon.
Mumm-Ra: Gary Oldman.

CGI or classic animation is who I'd cast. And then the above voices of everyone you chose, lol. Thundercats would come off as cheesy in live-action. What works in one meduim does not always work well in another, and thats when people nit-pick about the adaptation whether or not the film turns out to be good.

I'm not saying its a stupid idea or anything, I'm saying anyone who pulls off making a decent live-action film adaptation of the Thundercats would be a genius in my book.

But just for S & G's:

Lion-O: Gordon Shumway
Cheetara: Naomi Watts.*agree
Panthro: Samuel L. Jackson.
Voice of Snarf: Seth Mcfarlane.*agree
Tigra: Frank Oz
Mumm-Ra: Bill Cosby

I would cast all unknowns and put Peter Jackson in the director's chair

Lion-O: Hugh Jackman
Cheetara: Cameron Diaz
Panthro: Kelsey Grammer (he played beast in xmen, and panthro looks like beast.)
Voice of Snarf: Andy Serkis
Tygra: Vin Diesel
Mumm-Ra: Tim Curry