Strider: Ralph Fiennes
Best known for his role in Schindler's List, Ralph Fiennes is my pick for Aragorn the ranger (otherwise known as Strider). Aragorn is a character very burdened with his past, which would fit Fiennes perfectly, since he never seems to smile; he broods his way through most films like a modern day Nick Adams. Fiennes also has some action roles as well - he is set to play the lead in The Avengers (easily one of my most anticipated films of the year), and his brooding screen presence, and that unquantifiable regality that made him such a great villain in Schindler's List will serve the character well.
Boromir: Dennis Quaid
After his role as Bowen the Knight in Dragon Heart, Quaid seems like a no-brainer for the part of Boromir - at the very least, he knows his way around a sword. Like Quaid, Boromir is full of egotism and bravado; he acts as if he leads the party when in actuality he does no such thing. He would represent an excellent balance to Fiennes as well, which is key for the character dynamic between Boromir and Aragorn. And next, Gimli and Legolas...