Chris Russell over at Technology in Music Education has posted a collection of downloadable choral warm-ups. Special note for iPad users: As Chris mentions, you can embed the warm-ups into your presentation app (Keynote, for example) in order to mirror them to a TV, projector, or even all of the choristers’ iPads. By the way, Chris invites you to contribute your own choral warm-ups, in MusicXML or Finale format.
The Vaccai method books are another resource for vocal technique building that is now available online. You can download them for free in PDF format at either free-scores.com or IMSLP, in your key of choice.