Sol Weber also has a book titled Unofficial Set of Additional Rounds. Think I'd better invest in this one, too.

(A) Word to Husbands
ABC Round
Adam Catched Eve
All Is Silent (Mozart)
Alvin the Alligator
Ancient Walls
Angel Song
Anselm's Bread
Arms of Night
Aurora Borealis
Autumn Winds
Away In a Manger
Baby Lima
Baby Sardine
Beneath in the Dust
Black Sox
Blue Moon Quodlibet
Bona Nax (Mozart)
Cannon, The
Celia
Chug Chug
Cool of Autumn
Cow Round
Daily Bread
Dawn
Dirty Dishes
Distinctly Speak
Eagle, The
Early Bird
Early in the Mornin'
Easter Alleluia
Ecumenical Quodlibet # 1
Ecumenical Quodlibet # 2
Elephants
Et in Terra Pax
Faith (Mozart)
Family Grace
Father, Father Goodbye
Finney's Diner
Flow, Oh My Tears
Freedom Train
French Cathedrals (Fast Food)
(The) Frogs
Glory to God
(4-Way) Gospel Quodlibet
Grasshoppers Three
Guten Morgen
Halleluias (Maggie Gold's)
(The) Hart Loves High Wood
Have You Any Work for a Tinker?
Hey, Young Rider
Horsy, Horsy
How Great is the Pleasure
How Sweet to Be a Cloud
Human Nature
Humoresque/Old Folks at Home
If We Lose This Forest
Ireland, Ceili
Jesu, My Own Treasure
John, Came Kiss Me Now
Jolly Red Nose
Laughing Aurora
Lazin' in the Summer Sun
(A) Lazy Vicar
Let Freedom Ring
Listen
Little Boy's Prayer
Little David
Little Tommy Tinker
Lo, How a Rose
Loneliness
Love
Love, Love Sweet Love
Make a Joyful Noise
Man's Life's a Vapor
Marjorie
Martin Luther King Round
Matthew, Mark, Luke and John
(The) Merry Lark
(The) Moon Is Up
Moon Round
Mourn For the Thousands Slain
(The) Music Is Sounding
Musical Demon Quodlibet
My Bed Is Too Small
My Lady and Her Maid
Nero's Expedition
Notation
Now To All a Kind Good Night
0h, Beauteous Eyes
Oh, Fairest Maid
Oh, Let Thy Name (Billings)
Oh, Miss Lucy/Sweet Potatoes
Oh, Miss Smith
Oh, Mister Miller
Old Folks/Humoresque Quodlibet
Old Man From Calcutta
Peter Piper
(The) Pipe Round
Prisoners
Promises To Keep
Pussy's in the Well
Raindrops (Hej Pada Pada)
Red Earth
Rice Krispies (solo and round versions)
Roomph Roamph
Round For the Newlyweds
"Round Rounder" Round
Sad But True
Salute (Boyce)
Scip Scip
Seven Great Towns of Greece
Sing We This Roundelay
Soft the Evening Air/Boots
Sound Each Dulcimer
(A) Southerly Wind
Spring
Stadt Und Land
Star Wars
Sumner
Sweet Day
Swimming (Skiing?) Round
Taps
Test of Friendship
Three Blind Mice Are Dead
Three-Way Canon Blues
Time (Haydn)
To Electra (Haydn)
Trust
Turning Toward the Morning
Two Seeds
Twins
Tzena Tzena
Upward Trail, The
Vitamin C
Wake Ev'ry Breath
We'd Be In Less Danger
Where's the John?
Who Comes Laughing
Whole World
Who'll Buy My Roses?
Whose Pigs Be These?
Why Spend a Night
Windmill/Jubilate Deo
Winnie the Pooh
(The) Witch!
With Laughter and Singing