Weddingbee boards

I've never seen it done, but I have heard that you need to be careful about the species of butterfly you use because there have been problems with people releasing non-native insects.  These species can be invasive and cause harm to the surroundings.  So I guess you should find out which species are already native to your location before you do it.

you could light a rememberance candle, have a song played or do a reading or prayer in their honor.  (all cheaper and easier than releasing live creatures). You can also put a note in the program to acknowledge the person and explain the significance of the chosen reading/candle, etc...  If you are getting married near water, you could place a flower or wreath into the water.  I don't know if balloon releases are allowed in some places, but you could check.

As a biologist, I would highly, highly advise against it. Unless you are prepared to spend the day before running aroung collecting specimens from the area you will release them, you will be doing untold damage to the natural areas around where your wedding will be. not only can they kill off exsisting plants and other animals vital to the surrounding areas ecosystem, but you are releasing an animal that ususally has a large territorty between it and other butterflies in a close proximity...therefore the animals will spread, causing more damage, or possibly starve to death if they compete for food. 

I like other peoples suggestions, but would strongly advise against releasing ballons. while latex ballons biopdegrade, unless you use cotton, lightweight string, ribbon does not and is highly attractive to other animals that can choke on them. also if the ballon does not reach a certain altitude and burst it can come back to earth intact and be attractive as food to yet even more animals-killing or hurting them as well.