The Web. There are websites dedicated to song lyrics, some with chord symbols, some with music you can download as PDF files. I suggest you search Google or ask.com for "song lyrics." You won't find everything, but finding lyrics online is quicker than transcribing them from a recording.
For those who don't read music, you can scan music and create PDF files, then use PDFtoMusic software that you can download (including some free scaled-down versions) to listen to the music. The computer can even replicate the song lyrics, although often with off-kilter results. Search PDFtoMusic to find the software that best fits your needs.
Songbooks. John Feierabend created a series of songbooks for preschoolers, featuring bounce songs and ball-rolling songs, as well as songbooks for kindergarten and up, including The Book of Echo Songs,The Book of Canons, and The Book of Call & Response. These and many other books and CDs are listed in Resources.
The UUA offers four hymnals: Singing the Living Tradition; its follow-up, Singing the Journey; a collection of Choral Responses; and a wonderful new children's hymnal, May This Light Shine: A Songbook for Children and Youth. Both the teacher edition and the children's edition of this indispensable collection are available.
The UUA Bookstore (www.uuabookstore.org) offers collections like Sing Your Peace Songbook, Now Let Us Sing!, and Come Into the Circle: Worshiping with Children.
For Islamic and Hindu songs that children can sing and dance to, look for the songbooks published by Dances of Universal Peace (see Resources).
For Jewish songs for children, go to http://www.jewishmusic.com. This is the website of Tara Publications, a company that specializes in recordings and songbooks for all ages on all the many Jewish traditions. If you are looking for Israeli hip-hop or Yiddish Gilbert and Sullivan, Tara Publications will have it. I am particularly fond of The Harvard Hillel Sabbath Songbook (see Resources).
Songs of Zion is a wonderful collection of African American hymns, spirituals, and gospel selections. These include chapters that explain each tradition. I also love Dr. Ysaye Barnwell's Singing in the African American Tradition, a set of CDs on which she teaches the parts (mostly for more experienced singers).
There are more and more collections being released on CD and DVD, particularly from cultures that defy the Western tradition of written music. These are songs that are intended to stay within the oral tradition, a tradition of learning songs without the aid of hymnals or songbooks. More and more denominations are publishing collections of songs you can teach without hymnals. GIA Publications, for example, publishes several collections by John Bell of simple Christian songs from all around the world that children can learn by rote. In synagogues, the music of Shlomo Carlebach, with its simple yet passionate phrases, has grown in popularity. Many of these songs offer choruses in the niggun (nign) style. The niggun is a Chasidic wordless prayer that people sing and dance. Singers chant syllables like "Yoy yoy yoy" or "Dy dy dy." These wordless nigguns are considered the highest form of worshipful song and must be treated with utmost respect when they are used in worship.
Hymnals from other traditions are excellent resources. I am particularly fond of the old United Church of Christ Pilgrim Hymnal, the Shaker Hymnal, the Friends Hymnal, and GIA Publications' African American Hymnal (non-denominational). Your church probably has copies of out-of-print Unitarian (red) and Universalist hymnals, each of which includes wonderful old gems.
There are several excellent Earth-Centered songbooks, but some of them may be out of print. They are worth hunting down through used books outlets or Amazon.com. Look for Kate Marks' Circle of Song: Songs, Chants, and Dances for Ritual and Celebration; Julie Forest Middleton's Songs For Earthlings: A Green Spirituality Songbook; and a collection called For the Beauty of the Earth, an environmental songbook to benefit the Hudson River Sloop Clearwater. Libana's songbooks (with CDs), A Circle Is Cast, Night Passage, and Fire Within, are still in print (www.libana.com), as are Joanne Hammil's Rounds & Partner Songs, Vols. 1 and 2 (songbooks and CDs). This Ancient Love: Reflective Songs of Carolyn McDade, a collection of thirty-six early Carolyn McDade songs, is still in print—as are several of her CDs (www.carolynmcdademusic.com). Her 2007 CD, My Heart is Moved, is full of her new earth-centered hymns. I am fond of Jim Scott's Earth and Spirit Songbook: An Anthology of Songs Celebrating Earth and Peace. This book and his CDs are available at www.jimscottmusic.com. Jim Scott wrote several of the songs in Paul Winter's Missa Gaia/Earth Mass. (See Resources for more information about the above titles.)
Simplifying songs. It is often necessary to simplify songs for children. They obviously don't need to sing hymns in four-part harmony when the melody alone will do. The same is true of many choral pieces like the songs in Anders Nyberg's South African collections, including Freedom Is Coming. A song like "Thuma Mina (Hear My Prayer)" can sound lovely when a group sings it in unison. Children don't need to learn all the verses of songs with many verses. They can learn the chorus and one or two verses, while you or a singer from an older youth group sing additional verses.
While it is okay to simplify songs, be careful not to simplify other languages. Children are good at picking up languages as long as you don't try to do too much.
CDs and DVDs. Teachers who need to learn songs by rote (as opposed to reading music) love the Rise Up Singing songbook and its accompanying set of CDs. The book provides only the lyrics (except on rounds) and you learn the melodies from the CDs. A California company called Music for Little People sells many CDs (with no songbooks) of children's songs that you can play in the background or sing along with. I prefer singing with no instruments or CD backup, but for some, singing along with a CD is far less threatening. My favorite Music for Little People CDs are All for Freedom and I Got Shoes, by Sweet Honey in the Rock.
Mollie Stone, a conductor with the Chicago Children's Choir, provides a DVD called Vela Vela from which children and youth can learn South African songs by echoing and watching South African singers sing and dance. Anders Nyberg has two sets of CDs of great South African songs, with songbooks. For nonmusical readers who want to learn and teach new songs, the resources keep growing.
Popular songs. The Unitarian Universalist movement is not the first to use popular songs in worship. It is an old tradition. Martin Luther brought a German drinking song into the church by changing the words to "A Mighty Fortress Is Our God." After the Civil War, church musicians introduced the popular-song format, brought into common use by Stephen Foster, to their churches. This new format, including the gospel song "Shall We Gather at the River" (Singing the Journey, #1046), helped bring people back to the church. "Praise songs" are extremely popular in contemporary Christian worship, as are popular-song formats within Jewish worship. There are Jewish hip-hop artists who employ something they call heeb-hop.
This kind of new music isn't always welcome. Many congregants prefer the older prayers, hymns, and anthems. The best solution is to create a balance between the old and the new.