I was surprised to find my library subscribes to a service called Freegal...you can log in with your library card info and then download up to 3 MP3s a week at no cost to you. The count resets Sunday; I understand some libraries may run through their allotment by the end of the day Sunday or Monday.
When I investigated further, I found it may not be the best use of the library's money, as the library is often paying Freegal (who appears to work through Sony?) about $1 per MP3. But on the other hand, it also appears it's kind of a prepaid thing, so if your library has it, it's paid for and you might as well take advantage.
Christian artists include Switchfoot, Relient K, Fireflight, Nevertheless, Skillet, The Fray, and Red (you'll have to do Advanced Search for those last two). Certainly a ton more, but their browse option is absolutely abysmal so you have to search for a particular artist to find them!
Assuming you actually would've bought all these MP3s for $1 each, that's a free $156 a year...not too bad!
Now that I've saved you all that money, don't you want to go support a band who needs you? :)