There are so many resources for music and there's no wrong way to go. Let your music choices reflect and share your personalities with your guests. If you're into Icelandic Black Metal, you may want to consider something a bit more mainstream for your guests, but again, it's up to you. 
You will probably want something playing while your guests are arriving. Often music playing signals your guests that it's time to start. A quartet or a simple press of a play button can lead people to their seats. This music sets the tone for your ceremony. 
You'll want music as your bridal party enters. The length of this depends on the size of your party. It doesn't take long for a few people to enter, so consider natural breaks in the music to fade out for the next part of the ceremony. If you have a DJ or live musicians, they'll be prepared for this and keep an eye on the ceremony. If your cousin is wielding the ipod, make sure they know what you expect and how to work with the system at their fingertips.
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​These are some excellent choices I've heard for the bridal party processional.
  • The Beatles - All You Need Is Love
  • Ingrid Michaelson - Can't Help Falling In Love
  • Matt White - Love
  • Sara Bareilles - I Choose You
  • American Authors - Best Day of My Life
  • Jason Mraz - Love Someone
  • Buddy Holly - Everyday
  • Dave Matthews Band - You & Me
  • Natalie Cole - This Will Be (An Everlasting Love)
  • Train - Marry Me
  • Bruno Mars - Marry You
  • Jamie Lidell - Another Day*​    
There is no set in stone rule that the bride or groom need to walk in to a different song, but tradition marks the bride's entrance with a fresh piece of music that indicates someone important has arrived. Generally the guests stand during this entrance.
Here are some great songs I've heard used for the bride's entrance
Not many people have music during their ceremonies, but that's not to say it doesn't happen. One of the most amazing wedding moments I've experienced was when a brother and sister played guitar and sang for the bride and groom. He played guitar and she sang, "Can't Help Falling In Love With You"; it was breathtaking. 
The Recession! There's a kiss and cheering and an introduction of the couple...and there's celebratory music as the newlyweds take their victory lap. The bridal party follows and then parents and sometimes grandparents exit as well. 
The Officiant may or may not make an announcement during this music - again, an experienced DJ or live musicians will watch the ceremony and adjust accordingly. Then you're off to your reception!
While there are many choices for your
recessional music, this
is by far, my favorite:
Stevie Wonder's
Signed, Sealed, Delivered*


*These are links and I hope you enjoy.