Francis.
As noted elsewhere, my mother wanted to call me Francis but my father would not countenance such an extravagant name so it’s my middle one - unintentionally giving me the initials JFK.
I cannot imagine having gone through life as a Frank or a Francie instead of a Joe.
Sommer. A family name.
I’m a Lynn! I’m surprised we don’t have more of them here–I thought most women around my age (35) had Lynn, Marie, or Ann(e) for middle names.
Hal, have you and my husband been having secret meetings? I’m due in a couple of weeks and he’s still pushing Danger and Trouble. He is also fond of suggesting middle names that will give the baby funky initials - like KGB. He’s a bit nutty.
My middle names are Alexander and John, which is pretty amusing because my first name is Welsh and causes everyone to mispronounce and/or misspell it.
Following the family tradition, my kids (twin boys) have two middle names each as well.
Hartwell
All four of us kids got family surnames as middle names.
My wife would like to call me “Hart,” but I’m not convinced.
MacKenzie.
(Yes, with two capital letters. That’s how it is on my birth certificate.)
It’s a last name from a branch of the family that died out years before my birth.
Katrina.
Stratton
I’m 3rd generation oldest male with that middle name, and my sister gave the middle name to her middle son, seeing as I have no children and will never have any.
Carol (which is my mother’s first name)
Walton (father’s mother’s maiden name). I was named for my father’s father, whose middle name was Walter, but they wanted to honor the other side of the family while keeping the initials.
BTW: Every serious love affair but one in my life was with a woman with the middle name Marie. (The other one was Gayle. Go figure.)
Elliott. Same as my father, little brother, son and grandson. I am currenty fighting with a witch at a local Social Security office over my middle name. My official birth certificate from the county I was born has my middle name as Elliot. My middle name is spelled with 2 t’s on everything else. She is claiming I can’t get another SSN card till I fix this problem. Her boss tells me it doesn’t matter but in front of her he says it’s her call. I called back to Washington DC and was told it didn’t matter, I’m waiting for the official letter now.
I only mention it because there were a number of Dopers in some “names I hate” thread that said middle names like “Dawn” and “Lynn” were just fads, and they wanted to smack the mother or some such thing. I thought it was strange, but to each their own.
So, hello, fellow Dawn 
Paul.
I know, how boring, eh?
But I add my nickname right after it, and just before my last name on most things. Or, I just go plainly by my nickname.
Tripler
Oh, and I use the “Jr.” suffix, too.
Why thank you twickster and Priceguy on behalf of my parents. When I was knee high to a grasshopper, literally, my parents were living in a tent in the middle of the forest with no one else around for miles and hence had lots of time to come up with a good name.
I like the idea of 4 names but the last person to have that in my family died in 1908. Maybe I’ll revive it.
Walter.
My paternal grandfather’s first name. I never met the man, as far as I can recall; I assume because of that the name does not really have any significance for me.
Joy. No special reason for it, I think it was just a filler name. I often sign things Cyros J. MyLastName but rarely have any occasion to use my middle name. Meh.
My middle name is Kate. It was my great grandmothers name. Her name was actually Kate, not Katherine or Katrina- just Kate. I like my middle name.
My husbands middle name is Lee. he hates it.
Annette. And I’m surprised that I’m the only one so far.
Oooh, I like that. We’ve been struggling to find a middle name in case we have a girl (can’t start with a P, an L, a vowel or end in an N) Mind if I add it to my list?