Josh - You're doing a somewhat more youth-leaning format, aren't you?
If so, I
strongly second Groundwire and Lifeline Productions. Walk the Way is also pretty good, and is adaptable for younger or older audiences.
Ambassador Advertising is a good source and a good group to work with. However, pretty much all of their programming is more adult-targeted.
A couple more I'd recommend looking at:
Westar Media Group -
http://www.westarmediagroup.com - A syndicator, and another good group of people to work with. Most of their stuff is more adult-targeted, but they do have a few good offerings for younger audiences. (FYI, they are a syndicator for Walk the Way.)
Hotspots with Skip Heitzig -
http://www.hotspotsonline.net - 60-second spots. The production is hot, and the content is very Bible-teaching focused. May be exactly what you're looking for.
Reaching Your World with Luis Palau -
http://ryw.palau.org - 2-minute spots focusing on evangelism and encouragement. Would work for just about any Christian format.
Youth Waves with Blake Porter -
http://blakespeaks.com - Very youth-targeted 60-second teaching spots. However, they're not updated that often.
Not Religion -
http://www.notreligion.com - 30- and 60-second spots. They're not really Bible-teaching, but they're more designed to speak about life issues in a way that is relevant to both Christians and non-Christians. A very good evangelism spot.
888-NEED-HIM -
http://www.needhimresources.com - 30- and 60-second spots. Again, targeted toward evangelism. They have a very wide variety of spots for a wide variety of formats (some will work for your station, some probably won't). I believe they're updated at least monthly.
You might also want to look at artist testimonies. Some bands include testimonies or ministry tracks, usually as the last track on their CDs. (I know Disciple and Seventh Day Slumber each did this on one of their earlier CDs.)
Hope this helps!