Browsing around at my local game store the other day, I saw some tubes of FUDGE dice (dF, as they're called) and, since they were only $5.50 and I was in possession of a mere $12 in spending money, I went ahead and bought. I figured I'd probably never play it, but I like dice and can always use some weird ones laying around.
If you don't know, the dF is a d6, but instead of numbers, it has two sides with a plus sign (+), two sides with a minus sign (-) and two blank sides.
LOTS of really popular games, including Spirit of the Century and the Dresden RPG, use some variation of FUDGE, an open-source system.
What's neat about it is that it is purposely constructed for customization, and it seems easily scalable to a super-heroes game (I have never found a satisfactory system that replicated the big action of comic books, or that, in the Cape City game, can accurately reflect heroes as different as Overman and Gangbuster). So I'm seriously considering using it in the next Cape City campaign.
I won't bother trying to explain FUDGE myself, but I will copy/paste some stuff about it from Wikipedia:
"Rather than being a rigidly pre-defined set of rules like d20 System or GURPS, Fudge offers a customizable toolkit for building the users' own specialized role-playing game system. Such things as what attributes and skills will define characters are left to be determined by the Game Master and players, and several different optional systems for resolving actions and conflicts are offered. Fudge is not tied to any particular genre or setting and world builders are encouraged to invent appropriate attributes and rules tailored to the campaign.
Fudge characters can also have Gifts and Faults, which are positive and negative traits that do not fit into the adjective scale.
Fudge uses customized "Fudge dice" which have an equal number of plus, minus and blank sides. A number of these dice are rolled, usually four at a time ("4dF" in Fudge dice notation), and for every plus side that comes up the result of using the Trait is considered one step higher (e.g. from Fair to Good) and for every minus side that comes up the result is considered one step lower. The goal is to match or surpass the difficulty level, also on the adjective scale, of the test. Thus, a Good attribute is considered to be Great if you were to roll two plus sides, one minus side, and one blank—the minus side cancels out one of the plus sides and the remaining plus side raises the result by one step. The same Good attribute would be considered Poor if you were to roll three minus sides and one blank.
There are also several alternative dice systems available that use regular six-sided or ten-sided dice, coins, or playing cards.
The rules of Fudge are highly customizable and can be adjusted for the level of simplicity or complexity desired by the Game Master and Players. Overall, the system is designed to encourage role-playing over strict adherence to an arbitrary set of rules. In fact, the main Fudge documents encourage players to "Just Fudge It"; that is, to focus on the story being created rather than on the game rules. For example, one character creation method encourages players to first write prose descriptions of their characters and then translate those into Fudge Traits."