Dale Arden - Megan Fox (I know, way too easy) OR one of the Jessicas - Biel or Alba
Ming the Merciless - Jet Li (easy choice). He can do the physical work and just has to look evil. A bit short though. A more atypical choice? Vin Diesel. He has the imposing stature, menacing look, commanding voice, and can turn on the devil's charm while running you through with a sword.
Flash Gordon - Jason Statham. Athletic and versatile, just give The Transporter a ray gun and let the festivities begin! You say you want someone different? A "reimagination" of the classic hero? How about Dwayne "The Rock " Johnson? Having proven his mettle as a leading man and real actor, Johnson's charisma combined with his physical presence would make Flash "The Universe's Champion". "The Rock" Vs. Riddick - 'nuff said!
So, we conclude this evening's geek out session. Farewell from the New World.