Character Names

I love writing, but do you know what I find the most difficult bit? Naming the characters! I have lists and lists of girl's names and boy's names and I hum and haa over them until my head is in a spin. I've even held competitions for readers to name a character!
I pick one that I think is just right, for the character's age, personality, appearance, cultural background, role in the story and guess what? I've given all my main characters names beginning with the same letter or, as with my current work in progress, ones that rhyme!!Ridiculous.
Why is it so hard?