We have had great success with the Digioh app. It is very easy to use, and the lightboxes we've built using Digioh can be customized in a seemingly endless variety of ways (i.e., based on URL, geo-targeting, source, date, UTM code, etc.).
The support team is awesome to work with -- they've even built custom scripts for us -- and are always prompt and courteous in answering our questions.
Kay K., Children's Medical Center