The folks over at Sanctum Secorum recently did a podcast on Jack Kirby's Kamandi series and how it's deeply influential to the upcoming Mutant Crawl Classics RPG. In their podcast companion (available here for free) they offered a Kamandi-inspired Human racial class that represented them as feral and violent creatures. That got me to thinking: What would a Human race-as-class based on the common fantasy milieu look like? Keep in mind that this is very "broad strokes"/"brainstorming" post that isn't necessarily immediately usable.
General Concept: The keyword I would use for Humans in D&Desque fantasy is "versatile". Think about the fact that in OD&D and most versions of Basic D&D that Humans can be a whole slew of things (Fighting-men, Magic-users, Thieves, Priests, etc) while Elves, Dwarves, Halflings, etc. have much more limited options (the Mystara Gazetteers added extra slightly different racial classes for them).
Hit Dice: Probably a d8 per level. Tough but not too tough.
Arms & Armor: Humans are proficient with all arms and armor except for those unique to other races (no Dwarven urgoshes or Elfin chain for us). What a Human uses ultimately depends on his culture, wealth, location, and personal preference.
Base Attack Bonus: I use the 3.x terminology simply because I just don't like THAC0 that much. Humans aren't necessarily the fightiest guys around so their attacks and bonuses should probably progress as a Rogue/Thief (what 3.x called an Average Base Attack Bonus).
Magic Items: Humans can use any and all magic items they find but if the magic item has some kind of racial requirement ("Only Orcs can use this hat of hatred") then there's a 50% that item will be crumble to dust immediate after the Human uses it. For scrolls and other nerd stuff, treat the Human's HD as his caster level.
Clever Attack: Humans deal extra damage equal to opponents they catch unawares. This deals an extra 1d4 points of damage per point of Int bonus, to a minimum of 1d4 and maximum of 3d4 or thereabouts.
Animal Kinship: Humans have some sort of natural affinity for dogs and horses (or vice versa). These would translate to a +20%/+4 (depending on your skill system) bonus on checks made to befriend/clam/train/whatever such animals.
Animal Enmity: On the other hand, wolves and big cats (cougars, lions, etc.) hate Humans and will go out of their way to attack and/or eat them.
Destined for Greatness (?): Strange forces watch over Humans. Perhaps it is the will of the gods or the manipulations of more sinister forces. In any case, once per day a Human way re-roll any dice result.