I've been looking at slideshow apps for some time and have found them all to be pretty useful. Some of the iOS apps I've checked out don't let you choose transitions, and others have no way to let you choose your own music. So I was pleased to get a chance to look at Fliptastic, which comes with a variety of transitions and lets you select music from your own collection. The app also gives you a way to add attractive text to each slide. The downside is that there is a 10-slide limit, and a 15-second maximum length to your show. For a quick share, however, I can live within those limits.
Although the app says it's a slideshow maker for Instagram, don't let that deter you. You can save the videos to your camera roll and mail them