I can cause TV series to be canceled. All I have to do is decide I like the show. Works every time.
edit: oops
I just remembered one! I can tell if my farts will stink or not. Maybe other people have this ability also, but I’ve never really gotten around to asking. This calls for a new thread! —> http://boards.straightdope.com/sdmb/showthread.php?p=9772114#post9772114
My best one is I can blow cigarette smoke out of my ears if I try really hard, but it hurts like hell.
I can figure out how many letters are in a spoken word faster than anyone who has ever contested me. I was never really all that impressed with my abilities. But one of my friends is amazed and constantly sets up these contests against friends and strangers alike. I’ve won a few beers in bars over the years.
I can remember many, many street addys, emails, phone #s, voice mail #s, etc.
I can pee standing up and in a reasonably straight line.
I can imitate a number of accents and voices.
I don’t know if i’ll be able to express this properly: I flex the tendon that runs on the back of my thumb, and then snap my thumb back and forth along the underside of my index.
Or doing the flex thing, bending my fingers so they look like the figure seven, and wobble the first parts up and down (with my other hand, or i let others people try). Does that make any sense?
My knees bend backwards, like a flamingo. I can get them back probably twenty, twenty-five degrees from vertical.
Oh I forgot another one… if I turn my ankle to the side and rotate my foot, I can make a loud crunch noise as the tendon (or ligament?) scrapes over my ankle bone (artifact from post-astronomy accident ankle surgery). The main use for this is grossing my wife out. 
Were you knocked down by a rogue pulsar? Tripped over a meteorite? Dropped a chunk of neutron star on your foot?
I can do that to. I used to milk it as a kid, til my mom finally noticed that my “illnesses” conveniently coincided with dentist visits…
Looked up to see what was visible instead of down where I was stepping off the porch. :smack:
The tendon or ligament (can’t remember which it was) that gives lateral stability to the ankle snapped and rolled up inside my leg like a window shade… ouch. This effectively ended my pro-basketball career. 
I have a trick memory for movie lines (seriously, I see something once and it’s burned into my brain), and I’m a decent and unconscious mimic. When I quote movie lines, I’ll say it just like the character, only I don’t do it on purpose. I guess that’s just the way I remember it because that’s how it comes out.
I sort of count it as a secret talent, because I don’t do it on purpose. It’s kind of a secret to me until someone points out that, “wow, you sounded just like…”
Me too! Only it took me a minute to remember that Eustachian tubes and Fallopian tubes are not the same. A very confused minute.
I can make a clicky-tongue-noise that sounds like a galloping horse. This is only secret because if I can secretly use it to drive people insane. Click-click-click, click-click-click, click-click-click, OH GOD WHAT IS THAT NOISE.
I did that once, too. Plug your nose, close your mouth, blow hard. And yes, it hurts.
I can catch small snack foods thrown in the air, in my mouth. I can do it better if I throw it up in the air, but I can do it pretty remarkably well if you throw it in the air too.
As long as you’re not too drunk.
See, if I do that the smoke comes out my eyes.
It burns quite a bit, especially when wearing glasses.
I can do what I think is called a “clam tongue.” I fold in the edges of my tongue so that it looks sort of like a “W.”
I am not the girl in this video, but here is an example in case you’re not sure what I’m talking about.
Supposedly only a small percentage of the population can do this. I’ve only met one other person whom I knew for sure could do it, and that was my across-the-street neighbor when I was in fourth grade. She did it for my brother and me, and later I tried it and realized I could do it, too. I’ve only ever shown my “talent” to my SO, so I suppose that makes it a secret.
I’m pigeon-toed so the bones in my leg are both turned slightly inward. When I was little it was really obvious when I walked, but as I’ve grown older it’s self-corrected a lot. Regardless, we use to have to do this stretching exercise in gym class called the butterfly (see image here) in school. I’m a 30 year old guy and I can still pull my legs so far in that I can sit on my feet. I can also pull my feet back behind me, bending my knees, in such a way that it freaks everyone out. Yeah, I’m a popular guy.
I can flip my eyelids inside out…
Plus also, i give wicked massage.