I’m not talking about crazy stuff, like hocking a loogie 20 feet in the air and catching it with your mouth. I’m talking about abilities or qualities that are useful to humanity. Things that you have been complemented and depended on by your lovers, friends, and family.
My unusually enormously long penis generally makes a great impression, and is probably my greatest contribution to humanity. I get compliments on it all the time. “Hey, nice penis!” “Thank you.”
OK. I’ll be the first to ring my bell.
I’m very good in emergencies. I don’t panic; I have a weird kind of calm come over me.
Somehow, I immediately put aside the worry and panic and look to what needs to be done. Done NOW. All of the repercussions can be dealt with later, now, at this moment, we got to get our collective asses in gear.
I’m very, very good at staying calm.
Unfortunately, the little shit that happens every day can bug the hell out of me.
I find the truth.
Granted, I use the SDMB to do it a lot, but not always. I’m tenacious when it comes to fact checking, and finding things no one else can find (DVDs that supposedly ‘don’t exist’, long-lost school-chums, etcetera). It makes me proud.
I’m also pretty darn good with math, and I’m told I’m a hell of a storyteller.
Wow. I’m a geek.
I have a good sense of humor and always know what to say to make people laugh.
If I didn’t have this going for me, I’d have to say I was about the most useless person on the planet.
Like enipla I’m also very good during emergencies; I’m an excellent listener, especially when it comes to difficult emotional stuff (friends and boyfriends have told me this a lot); I’m an above-average singer; and I have solid writing and editing skills. All things that I’m regularly complimented on, so I’m not just being a legend in my own mind. 
Something I’ve only recently started getting noticed for is my leadership ability: this time last year I was nominated for my company’s annual leadership award, and just today I got a phone call from someone who wants to meet with me to discuss the possibility of my being a guest speaker at a local “women in leadership” group meeting. We’re having coffee after work on Monday. I’ve never imagined myself as a guest speaker, but I’m excited about the possibility! 
My husband pointed out to me that I have way above average determination. I did not really know that about myself - I thought everyone just gritted their teeth and hung in there until they got the result they wanted. He also called me the kindest person he’d ever met - again, did not really think of myself that way. I knew I was pretty empathetic, but kind? When I think about it, I suppose he’s right - I go out of my way not to hurt other beings.
And then there’s my ability to pick stuff up with my toes. 
My husband’s unique ability is the ability to watch ANY movie - and I do mean ANY movie. I’m not exactly sure how this contributes to the world as a whole, but there ya go.
I’m “the Dependable Guy”.
Plus I make people laugh.
I have perfect pitch. As far as the people I am acquainted with are concerned this makes me unique since I don’t know anyone else who has this ability. I can identify an F# with my ears just as easily as I can identify the color red with my eyes. Since nobody else has this ability they just have to take my word for it when I tell them what note a tone is. It would be like trying to convince everyone that the sky is blue if everyone else you knew was completely color blind.
I have “really blue eyes” whatever that means.
Me three.
I am also extremely easy going and good natured.
It’s almost impossible for me to be bored. Especially what with my fantasy world I mentioned a few months ago.
I’m elastic, able to fit into small containers, and can retain the colors from newspaper comics when pressed against them.
Shit, I’m thinking of Silly Putty. Me? I am, or I can be, sensitive, sympathetic, giving, and funny. I’m a skilled writer, and when I’m doing that, I can be articulate, observant and can say a lot about a subject. I’d say that’s the Greatest-Hits version of me. Take out the ridiculousness and that’s the good stuff.
I have amazing sideburns.
Their benefit to humanity is immeasurable.
A lot of friends and family call me when they have problems they can’t sort out. I can usually ask a few questions and break down the problem into a series of choices which make the solution seem obvious. For this I am sometimes called ‘Obvious Man’.
Also, I am a veritable font of totally useless information.
Oh, yeah, I also always know the ‘Wheel of Furtune’ answer before anyone else in the room–probably not a very unique ability among 'Dopers.
No one in my family uses a dictionary to check spelling or refers to a thesaurus for synonyms. They ask me instead. Of course, immediately upon clicking ‘Post Quick Reply’, I’ll see a spelling error in my post.
Oh, I forgot about my extremely interesting and fulfilling dream life. Just last night I had Stephen King over and was discussing his writing career with him (I got to tell him that his weakness was writing endings). I don’t know what benefit it is to humanity, but I sure enjoy it.
People say that I seem like an incredibly competent person–like I know exactly how everything ought to be done, and then do it. I do not feel this way myself, and I have never been called during a crisis, so maybe they are just making it up.
There is nothing I do, no quality I have, that is unique in itself.
Other people study the human form and desire to draw people better, other people make websites, other people are interested in solar-powered houses, other people speak Esperanto and English, other people are learning French, other people like to fool around with computers, other people are attracted to plump buxom women, other people live in Canada, other people read science fiction.
Now, the combination of those attributes may be unique (a website about solar-powered houses in Esperanto, anyone?), but there is no single thing.
I can eat any amount of food, for any duration of time, and still hold my borderline eating disorder weight. You want starving kids in Africa? I’ll make everyone starving, huzzah!
You, me, and 6 billion other people.