One of the best rounds collections for group singing (besides Sol Weber's books of course) is "101 Rounds for Singing" published by World Around Songs (formerly Cooperative Recreation Service). (These are the small 6 3/4" x 3 3/4" songbooks.) And it's still in print after all these years! http://www.worldaroundsongs.com/   I have a singing set of about 25 (they're small enough that everybody needs a copy).

Here's a somewhat annotated list of the contents.
I've tried to note composers and sources as cited. (Which may not always be correct, but that's another topic.)
I've listed the number of parts.   
Also, where the title given doesn't match the first line, I've included the first line to improve searching.
And where words are included in more that one language, I've tried to include each first line -- again to improve searches.

"101 Rounds for Singing" World Around Songs, Burnsville NC, (n.d.), 48 pp

Abenstille überall [Evening Still] (3 pt)
A Man With a Wry Nose (Richard Brown c 1735, 3 pt)
A Ram Sam Sam (Morocco, 2 pt)
Absalom (II Samuel 18:33, 3 pt)
Adieu, Sweet Amarillis (3 pt)
All Is Silent [German, and Engl tranl by Mex Exner] [Alles schweiget] (3 pt)
All Nature Smiles (Arnold, 3 pt)
And every man 'neath his vine and fig tree [Vine and Fig Tree] (2 pt)
Are You Sleeping? (4 pt)
At Summer Morn (3 pt)
Au Revoir, Amis [Now farewell, good friends] (3 pt)
Awake, Awake, Ye Dreamers (German, 3 pt or 6 pt)
Be Prepared (3 pt cumulative harmony; not a round)
Be You Strong [Rak chazak v'e matz] [incl Hebrew and English] (4 pt)
Bell Doth Toll (3 pt)
Bells of Old Haalem, The [incl French words] (3 pt)
Bento-Uri (Japanese vender's calls, 2 pt canon)
Blossom on the Plum (Max Exner, words from the poem "March" by Nora Hopper, 4 pt)
Bon Soir, Bon Soir (4 pt)
Buon Giorno (3 pt)
Canoe Round (Margaret Embers McGee 1918, 4 pt)
Chairs to Mend (3 pt)
Cherries So Ripe (4 pt)
Clocks, The [Store ure siger tik, tak, tik, tak] [in Danish] (3 pt)
Come, Follow, Follow (John Hilton 1599-1657, 4 pt)
Come Let's Be Singing [Hava Nashira] (English by M. V. Exner, 3 pt)
Congo Boat Song (3 pt)
Cost of Gladness, The (Swedish German round, English by Max Exner, 4 pt) [also in Swedish and German]
Derry Ding Ding Dason (3 pt)
Die Sonne sinkt [The sun descends] (3 pt)
Donkeys and Carrots [Donkeys are in love with carrots] [also in French] (Belgian round, 4 pt)
Earn a Little [Gagne Petit] [French words included] (2 pt)
Echo Yodel (Asutrian, 2 pt canon)
Ego Sum Pauper [incl English version] (3 pt)
Ein und zwanzig (2 pt)
Es tönen die lieder [With Laughter and Singing] (3 pt)
Evening Still [transl Max Exner; incl German words] (3 pt)
Fair Morn (3 pt)
Fellowship (2 pt)
Fray Felipe [Frère Jacques]
Fray Martin [incl Spanish words] (Latin American version of Lovely Evening, 3 pt)
French Cathedrals [Orléans, Beaugency] (3 pt)
Frère Jacques [also in French and Spanish] (4 pt)
Frogs [Hear the lively song of the frogs in yonder pond] (4 pt)
Froh zu sein, bedarf Mann wenig [The Cost of Gladness] (4 pt)
Gagne petit sur le chemin [Earn a Little] (2 pt)
Give to Me Your Hand [also in Dutch] (Netherlands, 16th cent., 4 pt)
Glad och god skall Mänskan vara [The Cost of Gladness] (4 pt)
Glide Along, My Bonny Boat (3 pt)
Good Morning to You (Max V. Exner, 4 pt)
Good Night, Good Night [Sweet Rest] (4 pt)
Good Night to You All (3 pt)
Grasshoppers Three (3 pt)
Happy Days (4 pt)
Hava Nashira [Come, Let's Be Singing] (English by M. V. Exner, 3 pt)
Hello to You (Reinhold Heyden, 4 pt)
Hey, Ho! Nobody Home (3 pt)
Himmel und Erde müsen vergehn [Music Shall Live] (2 pt canon)
Hiney Mah Tov (Psalms 133:1, 2 pt)
How Good and Pleasant It Is [Hiney Mah Tov] (2 pt)
Human Nature (words Johanna Ter Wee, tune Max Exner, 4 pt)
Hunger, Oh [Ach, wie furchtbar leer ist unser Magen] (Reinhold Heyden, 3 pt)
Hunter, The (3 pt)
Hunting Song [Merrily, merrily greet the morn] (4 pt)
Jane Glover [Go to Jane Glover and tell her I love her] (4 pt)
Joy in the Gates (6 pt)
Kookaburra (2 pt canon)
Laugh, Ha, Ha (4 pt)
Le soir descend [Evening descends] (3 pt)
Left, Right (Max Exner, 4 pt)
Les Ânes Aim' les Carottes [Donkeys and Carrots] (4 pt)
Les cloches de Haalem [Bells of Old Haarlem]
Let Us Sing Together (adapted from Czech Folk Tune, 4 pt)
Let's Be Beginning (Fritz Metzgen, 3 pt)
Light from a Star [includes German words](words Ludwig Schuster Engl by Max Exner, tune Hans Long, 4 pt)
List to the Bells (4 pt)
Listen to the Echo (Luigi Cherubini 1760-1842, transl. Ursula Stechow, 3 pt)
Little Bells of Wesminster (4 pt)
Little Bitty Man (Alabama, 4 pt)
Little Jack Horner (3 pt)
Little Tommy Tinker [Tommy Tinker] (4 pt)
Lo yissa goi el goi cherev [Vine and Fig Tree]
Lovely Evening [incl German words] (3 pt)
Lullaby Round (4 pt canon)
Make New Friends (4 pt)
Man's Life's a Vapor (3 pt)
Merrily, merrily greet the morn [Hunting Song] (4 pt)
Mi Y'malel? [Who Can Retell?] (2 pt canon)
Mill Wheel, The (Ichiro Suzuki, trans by Ichiro Suzuki, 4 pt) [incl Japanese transliteration]
Miss Crab (Ichiro Suzuki, 3 pt) [incl English transl and Japanese transliteration]
Music Shall Live [incl German words] (2 pt canon)
My paddle's keen and bright [Canoe Round] (4 pt)
Neemt Mij in de Hand [Give to Me Your Hand] (4 pt)
Nothing do I own [Ego Sum Pauper] (3 pt)
Now All the Woods Are Waking (Max Exner, up to 8 pts)
Now Farewell, good friends [Au Revoir, Amis] (3 pt)
O wie wohl is mir am Abend [Lovely Evening] (3 pt)
Oh, how lovely is the evening [Lovely Evening] (3 pt)
Orchestra (Estonia, 3 pt)
Orléans, Beaugency [French Catherdrals] (3 pt)
Owl in the Elm, The (2 pt)
Poor Tom [Have you seen the ghost of Tom] (4 pt)
Rally Song [Milha bilou loubi shembel] (Balkan, 4 pt)
Rise and Shine (Max Exner, 4 pt)
Rise up, O Flame (Christoph Praetorius, 8 pt)
Rose, Rose (4 pt)
Rosen fra Fyn (Danish round, 4 pt)
Row, Row, Row Your Boat (4 pt)
Scheinen die Stern [Light from a Star] (4 pt)
Seeyahnah (American Indian, 2 pt canon or 4 pt round)
Shalom Chaverim [incl Hebres and Engl] [Farewell, good friends] (2 pt canon)
Silver and Gold (tune Max Exner, Acts 3:6, 6 pt)
Sing Together (3 pt)
Singing School, The [I will sing you a song of the old Singing School] (3 pt)
Sommer Kommer [Summer's Coming] (4 pt)
Starlight, Starbright (Max V. Exner, 4 pt)
Store ure siger tik, tak, tik, tak [Clocks, The] (3 pt)
Summer Is A-coming In (4 pt canon, with 2 pt bass)
Summer's Coming (Danish, 4 pt)
Suze Naanje [incl Dutch and English] (2 pt canon)
The Swan Sings (4 pt)
Sweet Rest [Good night, good night] (4 pt)
Thou Poor Bird (4 pt)
Time Has Come, The (Czech folk tune; 2 pt canon)
Toembai (Israeli, 3 pt)
Tommy Tinker (4 pt)
Valamo Bells [Valamon kellosavelma] (2 pt canon)
Vine and Fig Tree [Engl and Hebrew] (Micah 4:3, 2 pt)
Wees Welkom [We welcome in the morning] (4 pt)
When a Weary Way You Find It (4 pt)
Where is John (F. Smetana-adapted, 3 pt)
Whippoorwill [Gone to bed is the setting sun] (Anne H. Chapin 1921, 3 pt)
White Sand and Gray Sand (4 pt)
Who Can Retell? [Mi Y'malel?] (Englsih words Dr. B. Edidin, 2 pt canon]
Wind in the Willows (4 pt)
With Laughter and Singing [Es tönen die lieder] [German words incl.] (3 pt)