Tell you the truth, most of my characters act like me. But I try and give them a personality acording to how they look and the name. Most of the time the personality comes to me as I write. 

Oh my gosh me too!! Well, so far I've only taken a personality test for one character. But it really helped, and I found out some things about her even I didn't know. I need to actually try it with the main character of the story though. XD

That's a cool idea about the avatar creator. To be honest, I have a really hard time imagining what my characters look like. Even envisioning their hair color/style is sometimes hard for me. I think an avatar creator would really help...I'll try that out next time I have some free time.

For my books, I love writing my characters into scenes that I'll probably never put in the finished novel. Just tiny 'fanfiction' scenes that are mostly dialogue and characters' actions, which I write when the mood overcomes me. When I'm inspired the characters just...flow better. Even if the scenes won't be put into the book, they really help.

I also make up scenes in my head, like movies, from all the different characters' points of view. (It's hard to do when you don't know what they look like though XD) I put them into situations where they meet each other and envision how it plays out. Usually I'll do it at night when I'm falling asleep, when thoughts flow through my head without a lot of effort.

The one book I actually do this stuff for has some of my favorite characters I've ever created.

My characters are usually based off people I know. I like to experiment a bit, though, like giving them personality traits of someone I like, and physical traits of someone I don't really like. Apart from making a great story, this helps me to be open minded and treat everyone fairly and kindly.