My college roomie had her guy walk down the aisle to meet her there to the Pixie's "Here Comes Your Man". GUSH PARTAY!I It was awesome and pretty punk rock in a funny way as the wedding was on a farm and she was wearing a HUGE ball gown.

Another friend walked back down the aisle to Queen's "We Are the Champions" and the audience jumped in to sing along. Really set a radical tone of fellowship and triumph! I had this idea first but she fell in love first, so all's fair in love.

Personally, if I were to make it offish with my partner then I would:

Walk up the Aisle to do the deed: "She's a Rainbow" by The Rolling Stones. It's so pretty and awesome and all about the lady! (Me in this case, radical). 

Walk Down the Aisle after the Ceremony to: Arthur Lee and Love's "Everybody's Gotta Live" for it's major mojo and romance; I think it also would set a righteous tone for a life together as well as a major rager reception.

First Dance: Janelle Monae's "Tightrope" -- I think it's very 'For Better or For Worse' not to mention would BRING THE INTERGALACTIC HEAT to the dancefloor. . . . Whether you're high or low. Baby whether you're high or low . . . .

If you choose any of those let me know because those are seriously the songs I would play.

My processional was the Chris Cornell version of "Ave Maria", our recessional was James Brown's "I Got You (I Feel Good)", and our first dance was Mark Lanegan's "I'll Take Care of You". I got a smartmouthed comment from my mom about "Ave Maria" ("you know that's about a virgin, right?"), but whatever, it fit us and our life together very well.

I plan on walking down to Brian Eno's 'Ending an Ascent', walking back out to Beach Boy's 'Feel Flows' and our first dance to Sam Cooke's 'Stand by me'

These are all my boyfriend I's most sentimental and personal songs, I think mixing generations and styles sets an amazing tone for the wedding :)

Our bridesmaids/groomsmen walked down the aisle to The Mountain Goats “Sorry mario, your princess is in another castle”
Flower girls: Franz Ferdinand “Do You Want To”
I walked down the aisle to: Maps “To The Sky”
Our first dance: Band of Horses “I go to the barn because I like the….” A close second (and almost was the song) is “Today” by Jefferson Airplane
My dance with my dad: Paul Simon “Father and Daughter”
My dance with my father-in-law: Jimi Hendrix “Little Wing” (a live version)
My husband danced with his mother: Iron and Wine “Upward Over the Mountain”
My husband danceed with my mom to: Seu Jorge “Life on Mars” (not lyrically meaningful, but we wanted Bowie) another good Bowie cover is M. Ward’s “Let’s Dance”

Hope this helps. I know picking songs can take forever! Good Luck!

Walk down the aisle:
*"E O Mai" (Keali'i Raechel)
*"Through the Kaleidoscope" Steven Cravis
*Language of the Heart" (David Wilcox)
*anything from Michael Gettel's "San Juan Suite" (the first one, NOT the second)
*"How Did You Find Me Here" (David Wilcox)

First dance:
*"Take It From Me" (the Weepies)
*"The Best is Yet to Come" (Frank Sinatra)
*"Better Together" (Jack Johnson)
*"World Spins Madly On" (the Weepies)
*"The Promise" (Tracy Chapman)
*"Gotta Have You" (the Weepies)
*"Heart of Mine" (Peter Salett)
*"Lucky Ball and Chain" (TMBG) (if you're brave)
*"Everywhere" (David Wilcox)

Unlike the other answers, I am not familiar with the different parts of the ceremony itself, but I would recommend the following songs in general for mushy feelings -

David Bowie - "Be My Wife"
Sparks - "Marry Me"
Magnetic Fields - "The Book of Love" (I personally would play "Take Ecstacy with Me")
Phyllis Dillon - "Don't Stay Away" (it is about unrequited love, but it is s beautiful song and the sentiment is sweet)
Betty Wright, "Just You"
Sugar Pie Desanto - "I Love You So Much"
Willie Nelson, "Can I Sleep In Your Arms"
Little Willie John, "Need Your Love So Bad"
Lefty Frizzell, "I Love You a Thousand Ways"
Solomon Burke, "I'm Hanging Up My Heart for You" (he will stop his slipping around for you)
Dusty Springfield, "Make It With You"

Tom Waits' "I Hope That I Don't Fall In Love With You".

We walked down the aisle to Pachelbel's "Canon," went back up it after the ceremony to the Grateful Dead's "Truckin'," and danced our first dance to Ben E. King's "Stand By Me." Worked for us (and we're still living happily ever after, 16 years on).

"I Want You" by Marvin Gaye or Robert Palmer.
"Evergreen" by Barbara Strisand
"Sexual Healing" by Marvin, again...
"I was Made to Love Her" by Stevie Wonder

This is the tentative plan:

Bride: Sigur Ros - Vaka

Recessional: The Books - That Right Ain't Shit

First Dance: The White Stripes - We're Going To Be Friends

We used classical music. The "walking down the aisle" music pretty much sets the tone for the rest of the ceremony. At the end of the day, pick a song that says something about you and your SO. There are no rules when it comes to the ceremony...

For a first dance, Steve Poltz - Everything About You (album version from "One Left Shoe", not the inferior "Notting Hill" soundtrack version)

Walking down the aisle, perhaps Erik Satie's "Gymnopedie no. 1" for a beautiful but not common walk.

Just what springs to mind at this time...