Well, not "lost" per se, but what Disney movies do you remember that don't get much love?

A few that I definitely watched a lot as a kid:
The Computer Wore Tennis Shoes
The Black Hole (absurdly dark for a Disney movie)
The Three Caballeros
Return to Oz
The Black Cauldron

Also, when trying to look these up, I had no idea just how many movies Disney made. I could have sworn I'd seen at least half of their movies, but... no.

1. 1937: Snow White and the Seven Dwarfs (G)
2. 1940: Pinocchio (G)
3. 1940: Fantasia (G)
4. 1941: The Reluctant Dragon
5. 1941: Dumbo (G)
6. 1942: Bambi (G)
7. 1943: Saludos Amigos
8. 1943: Victory Through Air Power
9. 1945: The Three Caballeros (G)
10. 1946: Make Mine Music
11. 1946: Song of the South (G)
12. 1947: Fun and Fancy Free
13. 1948: Melody Time
14. 1949: So Dear to My Heart (G)
15. 1949: The Adventures of Ichabod and Mr. Toad (G)
16. 1950: Cinderella (G)
17. 1950: Treasure Island (PG)
18. 1951: Alice in Wonderland (G)
19. 1952: The Story of Robin Hood and His Merrie Men (PG)
20. 1953: Peter Pan (G)
21. 1953: The Sword and the Rose (PG)
22. 1953: The Living Desert
23. 1954: Rob Roy, the Highland Rogue
24. 1954: The Vanishing Prairie
25. 1954: 20,000 Leagues Under the Sea (G)
26. 1955: Davy Crockett, King of the Wild Frontier (PG)
27. 1955: Lady and the Tramp (G)
28. 1955: The African Lion
29. 1955: The Littlest Outlaw
30. 1956: The Great Locomotive Chase
31. 1956: Davy Crockett and the River Pirates
32. 1956: Secrets of Life
33. 1956: Westward Ho the Wagons!
34. 1957: Johnny Tremain
35. 1957: Perri (G)
36. 1957: Old Yeller (G)
37. 1958: The Light in the Forest
38. 1958: White Wilderness
39. 1958: Tonka
40. 1959: Sleeping Beauty (G)
41. 1959: The Shaggy Dog (G)
42. 1959: Darby O’Gill and the Little People (G)
43. 1959: Third Man on the Mountain (G)
44. 1960: Toby Tyler, or Ten Weeks with a Circus (G)
45. 1960: Kidnapped
46. 1960: Pollyanna (G)
47. 1960: The Sign of Zorro
48. 1960: Jungle Cat
49. 1960: Ten Who Dared
50. 1960: Swiss Family Robinson (G)
51. 1961: One Hundred and One Dalmatians (G)
52. 1961: The Absent-Minded Professor (G)
53. 1961: The Parent Trap
54. 1961: Nikki, Wild Dog of the North (G)
55. 1961: Greyfriars Bobby
56. 1961: Babes in Toyland
57. 1962: Moon Pilot
58. 1962: Bon Voyage
59. 1962: Big Red
60. 1962: Almost Angels
61. 1962: The Legend of Lobo (G)
62. 1962: In Search of the Castaways (G)
63. 1963: Son of Flubber (G)
64. 1963: Miracle of the White Stallions
65. 1963: Savage Sam
66. 1963: Summer Magic
67. 1963: The Incredible Journey (G)
68. 1963: The Sword in the Stone (G)
69. 1963: The Three Lives of Thomasina (PG)
70. 1964: The Misadventures of Merlin Jones (G)
71. 1964: A Tiger Walks
72. 1964: The Moon-Spinners (PG)
73. 1964: Mary Poppins (G)
74. 1964: Emil and the Detectives
75. 1965: Those Calloways (PG)
76. 1965: The Monkey’s Uncle
77. 1965: That Darn Cat! (G)
78. 1966: The Ugly Dachshund
79. 1966: Lt. Robin Crusoe U.S.N.(G)
80. 1966: The Fighting Prince of Donegal
81. 1966: Follow Me, Boys! (G)
82. 1967: Monkeys, Go Home!
83. 1967: The Adventures of Bullwhip Griffin
84. 1967: The Happiest Millionaire (G)
85. 1967: The Gnome-Mobile (G)
86. 1967: The Jungle Book (G)
87. 1967: Charlie, The Lonesome Cougar
88. 1968: Blackbeard’s Ghost (G)
89. 1968: The One and Only, Genuine, Original Family Band
90. 1968: Never a Dull Moment (G)
91. 1968: The Horse in the Gray Flannel Suit
92. 1969: The Love Bug (G)
93. 1969: Smith!
94. 1969: Rascal
95. 1969: The Computer Wore Tennis Shoes
96. 1970: King of the Grizzlies (G)
97. 1970: The Boatniks (G)
98. 1970: The Aristocats (G)
99. 1971: The Wild Country (G)
100. 1971: The Barefoot Executive (G)
101. 1971: Scandalous John (G)
102. 1971: The $1,000,000 Duck (G)
103. 1971: Bedknobs and Broomsticks (G)
104. 1972: The Biscuit Eater (G)
105. 1972: Napoleon and Samantha (G)
106. 1972: Now You See Him, Now You Don’t (G)
107. 1972: Run, Cougar, Run (G)
108. 1972: Snowball Express (G)
109. 1973: The World’s Greatest Athlete (G)
110. 1973: Charley and the Angel (G)
111. 1973: One Little Indian (G)
112. 1973: Robin Hood (G)
113. 1973: Superdad (G)
114. 1974: Herbie Rides Again (G)
115. 1974: The Bears and I (G)
116. 1974: The Castaway Cowboy (G)
117. 1974: The Island at the Top of the World (G)
118. 1975: The Strongest Man in the World (G)
119. 1975: Escape to Witch Mountain (G)
120. 1975: The Apple Dumpling Gang (G)
121. 1975: One of Our Dinosaurs is Missing (G)
122. 1975: The Best of Walt Disney’s True-Life Adventures (G)
123. 1976: Ride a Wild Pony (G)
124. 1976: No Deposit, No Return (G)
125. 1976: Gus (G)
126. 1976: Treasure of Matecumbe (G)
127. 1976: The Shaggy D.A. (G)
128. 1977: Freaky Friday (G)
129. 1977: The Littlest Horse Thieves (G)
130. 1977: The Many Adventures of Winnie the Pooh (G)
131. 1977: The Rescuers (G)
132. 1977: Herbie Goes to Monte Carlo (G)
133. 1977: Pete’s Dragon (G)
134. 1978: Candleshoe (G)
135. 1978: Return from Witch Mountain (G)
136. 1978: The Cat from Outer Space (G)
137. 1978: Hot Lead and Cold Feet (G)
138. 1979: The North Avenue Irregulars (G)
139. 1979: The Apple Dumpling Gang Rides Again (G)
140. 1979: Unidentified Flying Oddball (G)
141. 1979: The Black Hole (PG)
142. 1980: Midnight Madness (PG)
143. 1980: The Last Flight of Noah’s Ark (G)
144. 1980: Herbie Goes Bananas (G)
145. 1981: The Devil and Max Devlin (PG)
146. 1981: Amy (G)
147. 1981: The Fox and the Hound (G)
148. 1981: Condorman (PG)
149. 1981: The Watcher in the Woods (PG)
150. 1982: Night Crossing (PG)
151. 1982: Tron (PG)
152. 1982: Tex (PG)
153. 1983: Trenchcoat (PG)
154. 1983: Something Wicked This Way Comes (PG)
155. 1983: Never Cry Wolf (PG)
156. 1984: Tiger Town (G)
160. 1985: Return to Oz (PG)
161. 1985: The Black Cauldron (PG)
162. 1985: The Journey of Natty Gann (PG)
163. 1985: One Magic Christmas (G)
164. 1986: The Great Mouse Detective (G)
165. 1986: Flight of the Navigator (PG)
166. 1987: Benji the Hunted (G)
167. 1988: Return to Snowy River (PG)
168. 1988: Oliver & Company (G)
169. 1989: Honey, I Shrunk the Kids (PG)
170. 1989: Cheetah (G)

I stopped right before The Little Mermaid because the site I am using for reference also includes movies that Disney picked up (like Touchstone), technically making things like Gross Anatomy part of the Disney movie collection. Then gets more absurd with the addition of Marvel and Star Wars.