“Caroline”, because my wife found a reference that said it meant “joyful song” and because it went well with the first name, “Sophia”, which means “wisdom”. So, wisdom, joy, and song is the foundation of our daughters name and we’ve definitely hit it right on the head in regards to the latter two - time will tell about the first.
But we’re trying. 
Kei.
His first name is very similar to mine, so for his middle name we used one of the kanji from his mother’s name.
A joyful song, or a sweet song? http://www.youtube.com/watch?v=JMTgiFedLpE&feature=related
See, I think having multiple middle names is cool. However, after we came up with oldest son’s middle names and started parading them around, I was told that it’s pompous and pretentious to have two or more middle names. If I have a third child, s/he should have three middle names just to throw everyone off. Or none!
Oldest – Paige, just because we liked how it went with the first name
Middle – Elizabeth, because it was generations and generations traditional on my side, and I wasn’t about to mess with tradition
Youngest – David, because it’s his daddy’s name
Hunter after Hunter Thompson.
My daughter’s middle name is Vaughn since our last name is German.
My son’s middle name is Harrison, a good pretentious name if he ever does the first initial, full middle name thing like H. Ross Perot.
My older son’s middle name is Alexander. Mainly we jus liked the sound of it with the first name we picked out; it’s also a traditional first name in my wife’s family.
My younger son’s middle name is Christian, same as his dad’s. 
(My parents gave me that middle name because I was born on Easter Sunday.)
My daughter was born in December–her middle name is Noelle. Her first name is Sandra. Sandra Noelle has a nice ring to it. Plus, if she gets tired of Sandra, she can go by Noelle if she wants.
Michael, Matthew, and James - just because they sounded right when stuck between their first and last names. I almost wish there was more of a story to them.
Elizabeth. It was the first name of both my Mother and Mother-in-Law
My kid’s both have my wife’s pre-marriage name as their middle name. It’s a Thai last name. Mrs Shibb also made that her middle name when she took my last name*.
The main reason for this was to maintain a part of their Thai heritage. Also kept me from having to come up with something clever. My middle name is my grandfather’s (Anglicized) first name. Many of their cousins have names following similar conventions.
*Mrs Shibb keeps her family name on her Thai passport. This has turned out to be useful, since the rules for property ownership in Thailand require that you be Thai, and a Thai name is part of being Thai. It’s a little more complicated than that, but this may also help my daughter at least to later inherit property in Thailand. We’ve not registered my son as Thai as Thailand has compulsory military service for males.
I have an intense dislike for all middle names that are common middle names: Ann. Jo. Sue. Lyn. Marie. Very rarely do they make for a pleasing combination and it just seems like such a waste… Pick a real name that is interesting and/or meaningful.
My middle name is Lyn. It’s actually not so bad as a first name. But it just seems like such a space filler as a middle name.
Hmmm I think this is the first time I’ve participated in a “Doper Parents” thread. The baby is going to be three in a few weeks and I still don’t think of myself as a Dad.
Anyways, Baby P’s name has no family references at all. At some point in my life I mentioned to my now wife/then GF that I like the name Juliet.* She remembered that I said that and decided that should be the name of the little one, Emily as a middle name just sounded good, and there we have it Juliet Emily P.
Oh, I forget, both my and my wife’s initials are JEP, so since we had chosed Juliet as a first name, my wife decided the middle name should be an E name as well.
I’ve never read Romeo and Juliet, I really dislike Juliette Lewis and I know she’ll get a lot of crap for the name*, but I still like it.
**That didn’t dawn on me until long after we had named her, kind of a doh moment when I realized it.
My older daughter’s middle name is Eve. She was the first female grandchild in my family.
My second daughter’s name is Gabrielle. I wanted to name her for an angel, & name lists tell me that the name is the fem for Gabriel, “archangel, ‘fighter’”. This fits my “wild child” daughter.
Love, Phil
My daughter’s middle name is Rose, as well, and I think you are right about its trendiness! I like it, though. I picked it partly for religious reasons, and partly as a little tribute to two of my personal heroes…Laura Ingalls Wilder, and her daughter, Rose Wilder Lane.
My son has two middle names…Paul is the one we had originally picked, and we added my grandmother’s maiden name when we realized he was born on her 100th birthday!