Also I usually make mine up as I go along. I tend to get a kick out of it when people compliment me on how well thought out my character is when I just c+p the sign up sheet into a reply and start making crap up off the top of my head. :D
Oh, I know that feeling. I sometimes have a character idea for either species, appearance, very basic personality, or some bizzare quirk and just make the rest up. Then I go back and tweak it a couple of times so it doesn't seem so random, and there you go.
But, yes, trends. Well, plently of people who have roleplayed with me know that my characters are always female, except on very rare occasions with non-humans. I'm not sure why, exactly, but I just more easily take on the role of someone my own gender.
I have some basic personality types that I have, which I'll list because I like listing things (appearance applies to humans, of course):
Number One-The short, but extroverted and slightly eccentric types. Usually loud, mischievious, and sometimes mildly flirty. I like going with red hair and freckles, but sometimes a well-tanned blond (who's not quite as short) takes the role well.
Number Two-The cold, get-the-heck-out-of-my-way-or-die types, usually excelling in hand-to-hand combat and wearing all black. They don't want to be talked to, they don't want to be touched, and are usually tall, pale, and have strange-looking eyes.
Number Three-The misunderstood girls who look like number two, but act more like number one. Gothic shells with friendly souls, albeit usually with a slight competitive or rebellious streak.
Number Four-The sarcastic 'straight man' who usually is smart and bookish, but not the least bit shy and is more than willing to use her vocabulary to come up creative ways to describe things and make comebacks. Usually brown-haired with large glasses and appear shy at first until they have something to say.
Number Five-The cute, niave type. I don't have many of these characters, but they're still kind of fun. Akward and often non-humans in a human place, they stumble through things and fail to understand the meaning behind words and expressions, but put them in their element and they suddenly seem superintelligent.
Number Six-Similiar of number two, but worse. Number twos generally have a heart somewhere, but these are complete pyschos. Pale, empty eyes and no remorse, these are a hard one for me to keep in character, but I still like the challenge.
Number Seven-The ones that seem completely out of left field. The ones that I have no idea where they came from. The ones with a very long 'Other' section on the sign up form.
But I break the mold so many times, I don't even know if the descriptions there even apply to half of the characters I consider of those types.
The only thing I repeat on a regular basis is names. I can think of four characters of mine that have the name 'Shannon,' let alone 'Chris' or 'Alex.' Descriptive nicknames are my best friend, I tell you.