Origin Archetypes
Generally speaking, every comic book character with access to powers or abilities above and beyond normal people fits one of four archetypes for the origin of their swank new abilities. These are described in detail below. Origin events will occur during play, so this is giving the players control over the source of their powers without actually having to write up the specifics on the origin.
Note: Even though Powers are the last step, and are acquired post-origin, it is best to think about what type of powers you want your character to have and propose them as soon as possible so that The Producer can give you any details as to the plausibility/acceptability of what you are looking for. Players are advised to think of powers they want their characters to have and not look at any of the source material. Powers in the source material, especially the Ultimate Powers book, tend to be obscenely broken. If you base your powers off of what you read from one or more in that book, do not expect them to be nearly as effective as is stated. This is a low-power game.
"Circumstances conspired to make me what I am."
Something happened, and now your character is different. Maybe it was even your character's own science experiment gone awry. Whatever the event, it was not in any way intentional.
Examples: Spiderman, Hulk, The Flash, Daredevil, Joker (Tim Burton's), Dr. Manhattan
"I was chosen for this path."
Someone or something looked at all of the beings on the planet and decided that your character, above all others, was the one who would receive this power. This could have been something your character wanted (or even knew), secretly, their whole life, or they could be completely in the dark about why they were chosen. It could even be unwitting (such as in the case of many vampires and werewolves).
Examples: Green Lantern, Buffy, Captain America (though he technically had a choice)
"I was just born this way."
Your character does not know it yet, but they were born different from normal people. They have been different their entire life. There was no choice, nor an outside influence other than the circumstances of your birth.
Examples: Mutants, Thor, Superman, Wonder Woman, Ozymandias, J'onn J'onzz
"This is the path I chose."
Your character knew what they would be getting into, or at least thought they knew, and made a conscious decision to abandon a normal life in favor of one where they are at odds with greater forces. The character could have been building towards this all along or could have been faced with a choice, superpowers of some flavor on one end of that choice. Whatever the specifics, your character chose to be what they became.
Examples: Iron Man, Rorschach, Batman, Doctor Strange
Power Source Archetypes
Your character's special nifty abilities have to come from somewhere. They will be getting their powers during play, so bear this in mind. This is just to help figure out where people want to go with their powers so I can plan accordingly. Characters with "Learned Power" archetypes will have a sudden breakthrough to justify a sharp increase in ability from a normal person.
Innate Power
Your character's powers are contained within themselves. They are a part of them as much as an arm or a leg.
Advantage
No obvious way for powers to be taken away (your enemies can't just come in and sabotage your super suit or something). Attribute and power enchancement is at the normal rate.
Disadvantages
Innate powers typically come with an innate weakness (J'onn J'onzz is weak to fire, Superman is weak to kryptonite, most versions of the Hulk cannot control their transformation). It does not have to be some kind of material or lack of control, however. It can also be that your powers were given unto you by, say, someone in the Greek pantheon or something, and they can revoke those powers at any time. Also, acquisition of new powers is extremely costly, as new powers typically do not spontaneously develop.
A character with an Innate Power can elect to "buy off" their weakness by taking a percentage penalty to the points given for advancement (those points are being spent every time to buy the "not having a weakness" trait). It can be thought of as a balance tax.
Examples: Thor, Superman, Buffy, J'onn J'onzz, Spiderman (Ultimates line), Dr. Manhattan, The Flash, Mutants
Tech Based Power
Your character's powers are the result of gadgets, gizmos, ancient artifacts, the Crimson Gem of Cyttorak, etc. They come from a material source.
Advantage
New powers are less costly. They may be somewhat difficult to acquire in other ways (need to purchase materials or go on a hunt for another piece of your incomplete artifact or whatever), but as far as using advancement points goes they will be much cheaper than standard. Attribute and power enchancement also costs less if the power-suit route is used, up to a point (your character just needs to get more power out of the engines for more powerful flight ability, or needs to get the torque improved in the joints for more strength, etc).
Disadvantages
You can be without your material goodies, leaving you in a "normal joe" state, effectively. Also, you can be subject to equipment malfunction, design flaws, the effects of magical flux on your shiny wubba wubba, etc.
Examples: Green Lantern, Iron Man
Learned Power
Whatever it is your character has, they got it through hard work, study, and testing their limits. There was no accident, there are no tools of the trade, the character was not born better than everyone else. Maybe your character has learned the arts of magic. Maybe they train religiously every day in an effort to be a great martial artist or scholar or socialite. Obviously certain origins are harder to apply to this archetype than others, and certain powers/abilities are harder to justify.
Advantage
No weakness. Nothing can take away what your character's hard work has won them.
Disadvantages
Lower upper limit to powers than other archetypes. Acquisition of new powers is expensive AND time consuming, typically beyond the realm of plausibility. Attributes are capped at human maximum. Improvement of powers and attributes requires extensive training time.
Examples: Daredevil, Rorschach, Ozymandias, Doctor Strange
Hybrid Power
This is meta. Your attributes come from one archetype listed above, but your powers come from another. Each has the specific advantages and disadvantages for that aspect of your character. Hybrid characters with Innate Power for one of their aspects only pay half of the "advancement point tax" for electing not to have a weakness.
Examples: Batman = Learned Power [Attributes] Tech Based Power [Powers], Wonder Woman = Innate Power [Attributes] Tech Based Power [Powers], Spiderman (Classic with Webshooters) = Innate Power [Attributes] Tech Based Power [Powers], Captain America = Innate Power [Attributes] Tech Based Power [Powers]
Note: If anyone can come up with an example from comics or popular superpowered media where a character has what would be classified as a combination of Innate Power for one aspect and Learned Power for another please let me know so I can add it/them to the list of examples.