I used a spark to build a Dr Who themed “timey wimey” machine. The user can select a day / month. The sprak will look up said they on wikipedia, select a random fact, and have The Docter speak that fact using an EMIC2 text to speech breakout board.
I entered it in the instructable & spark “enchanted objects” competition, you can find the instructable here:
I use a musicmaker shield to play the tardis-time-travel sound and had some issues with the converting the libraries. See this thread on the (ongoing!) help I got from this community: http://community.spark.io/t/adafruit-vs1053-mp3-library-for-music-maker-shield-ported/
For Dutch people: I wrote a column about building this project in the newspaper De Volkskrant, in the Sir Edmund section. It will be published on december 13th.