I have done few things involving Make A Wish but never organized anything.
A few years back I worked as a ground transportation coordinator at the Port of Los Angeles working mostly with cruise ships. Since the job involved being somehwhat close to those in charge of the ships activities along with those that run the port I was able to arrange special check ins for the guests, room upgrades and local tours of our port town and every port on the itinerary at no cost thanks to the ships purser. What got to me was hearing why a kid would want to go on a cruise instead of something the likes of Disneyworld. The same cruise was where his parents went on their honeymoon and the kid was "made" (his word). The ships Purser went as far as he could to have things done for the guests all the way up to securing the exact same room they had stayed in on the honeymoon with the help of the passengers origianly assigned that room who were also on a honeymoon. Those guests if I recall were given the best room available for the gesture.
It was awesome, things that are so simple as courtosy from others can make a persons wish's come true.
There was another where the child wanted to be a Jedi in a Star Wars movie but the new trilogies were between films. LFL contacted the fan organization "the 501st" and arranged to have Mark Hamill meet with the group while filming a fanfilm sequel to "Pink 5". I wasnt there for that one but did help make props for it.
click here for pictures: Make A Wish SW
Being part of the 501'st we also do childrens hospital visits and others have done numerous Make A Wish apperances as costumed Star Wars characters on behalf of LFL around the world. Wished there was more pictures but generaly we are behind costumes and in character for the kids which makes it difficult to take pictures on our side.
click for pics of CH visit
There are also events for ICAN, City of Hope, Childrens Miracle Network, Toys for Tots...
If you can take part of any event, trust me, its well worth it. Even the slightest effort helps.