So, I'm going to go over MY criteria for what makes characters memorable for me.
NOTE: This really applies to what I think makes a memorable hero (villains are a whole 'nother ball game that maybe we can handle in another week).
1) I'm a bit on the fence about complaints. I don't like whiny emo people (exhibit A: Harry Potter in Book 5). If you're going to be whiny, at least have a sense of humor about it. If you're going to be whiny and not be funny, then you are no longer memorable to me. In fact, I don't even know if I'm going to finish reading your story, dear MC. I finished HP5 barely, because I had already invested 1000+ pages of love in Mr. Potter, and if he was going to have his hormonal cry-fest in one book, well, then I could deal with that.
2) Be a person of action. Don't let action happen to you. You are the hero! Do something, go somewhere, kick some ass. Because if you're not, then maybe you should switch places with your sidekick and save us all the trouble of suffering through x-pages of watching you get your backside slapped around by circumstances out of your control. Nobody wants a weak hero. You're not even real, so do something that will impress me and make me remember you. Do something that nobody else would do.
3) Really noble people. I will admit, this is blatantly something that applies directly to me. It is entirely possible that you like heroes who run in shades of gray (which is fine; I like them too, but not so much as the noble ones). I find that I particularly like heroes who are always striving to do the good. Who are rarely conflicted by TEH EVIL even if it threatens to win overwhelmingly. Who doesn't like a good stalwart underdog? My theory as to why I prefer noble heroes is that the world needs noble heroes, and they always seem to be the ones people admire the most, you know? It takes a lot to be so committed to the light.
So there it is. Here are some of my favorite heroes, in no particular order:
1) Harry Potter
2) Ella (Ella Enchanted)
3) Scarlett O'Hara
4) Percy Jackson
5) Coraline (Coraline)
6) Esperanza (Esperanza Rising)
Hmmm. It occurs to me that I should read more books with male protagonists. I will work on that.