Harry's eyes are described bright green, and this
fact is said thorought all the books so many times,
that it should be natural.
Ron's eyes are described blue, and I thinks this kind
of really bright blue would fit with his hair the best.
Hermione's eyes are described brown, and I imagine
them to be warm chocolate kind of brown.
We don't know any specifics about Neville's eyes,
but in the movie he's got grey-blue eyes, and I
think those fits him.
Ginny's eyes are described brown, and in my opinion
a darker brown would fit her better, rather than
choclate brown what Hermione has.
Draco's eyes are described grey, and they look just
perfect in the movie, light steely grey with maybe
a little hint of blue.
Luna's eyes are described to be silvery grey, but in
the movie they are blue (and I absolutely adore
Evanna's Luna in the movies). I kind of mixed them
together giving her silvery blue eyes with a little hint
of purple.
Voldemort's eyes are described red, and what could be
more fitting than rich blood red.