I spend an inordinate amount of time naming my characters. I'd say it's almost like giving birth, but then I have no clue what that is like so I'll just say it's both wonderful and painful.
Sometimes I go for the sound of a name, sometimes I research meanings and search for a name that expresses what that character means, either to me or the plot. Very, very rarely does a character come to me pre-named.
Case to point, the two MCs in my current WIP are called Tay, Rho and Doyle - or, to forgo nicknames, Aletheian, Minoro and Feardorcha. The first two are adaptations of "truth" in different languages. Feardorcha means something along the lines of 'the dark-haired man' (Doyle means 'dark stranger' or some such, in case you were wondering).
How do you name your characters? Do you name them once and leave it at that? Does the name sometimes change as your plot evolves? Do you take the first name that occurs to you, the first one that sounds good?