Yucca treculeana canaliculata x Yucca recurvifolia  (= Yucca treculeana x Yucca recurvifolia)

Yucca X Elwesiana
Yucca X Fosterana
Yucca X Lawrensceana
Yucca X Diana

Yucca treculeana canaliculata x gloriosa (=Yucca treculeana x Yucca gloriosa)

Yucca X Minerva

Yucca gloriosa x filamentosa

Yucca X Nicotrana (no pollen)
Yucca X Rex (Yucca gloriosa minor X Yucca filamentosa)

Yucca gloriosa robusta x flaccida

Yucca X Dux

Yucca gloriosa longifolia x flaccida

Yucca X luxurians

Yucca gloriosa plicata x Yucca recurvifolia

Yucca X Darwinii

Yucca flexilis x filamentosa

Yucca X Augusta

Yucca flexilis x flaccida glaucescens

Yucca X regalis

Yucca filamentosa x flexilis

Yucca X Saturnus

Yucca flaccida x flexilis

Yucca X Gaea

Yucca rupicola x gloriosa

Yucca X aletrodes

Yucca rupicola x Yucca recurvifolia

Yucca X Sokrates

Yucca filamentosa x Yucca rupicola

Yucca X liliacea
Yucca X Psyche
Yucca X Treleasei

Yucca flaccida x Yucca rupicola

Yucca X amonea
Yucca X Atropos
Yucca X paradoxa

Yucca aloifolia x filamentosa

Yucca X Adenophora
Yucca X fastuosa
Yucca X Ismene
Yucca X linearis
Yucca X linifolia
Yucca X virescens

Yucca aloifolia x flaccida

Yucca X Candolleana
Yucca X columnaris
Yucca X Oceanus
 

Yucca aloifolia x Yucca rupicola

Yucca X smaragdina

Yucca aloifolia x Yucca gloriosa

Yucca X Europa
Yucca X Naudiniana
Yucca X vomerensis

Yucca aloifolia gigantea x Yucca recurvifolia

Yucca X Heliodorus

Yucca aloifolia purpurea x Yucca recurvifolia

Yucca X Victor Emmanuel II (Vittorio Emanuele II) Link to photo outside bennyskaktus.dk

Yucca aloifolia x flexilis

Yucca X Casertana
Yucca X Helios
Yucca X Sieheana

Yucca aloifolia marginata x flexilis

Yucca X Titanus

Yucca filamentosa x Yucca aloifolia

Yucca X Ada
Yucca X Alexandrae
Yucca X Boissieri
Yucca X Dohrnii
Yucca X tulipfera
Yucca 'Washington'

Yucca flaccida x Yucca aloifolia

Yucca X Draco
Yucca X Mariea
Yucca X pygmaea
Yucca X pyramidalis
Yucca X Roland
Yucca X stellaris
Yucca X Theseus
Yucca X tortilis

Yucca flexilis x Yucca recurvifolia

Yucca X grandis
Yucca X superba

Yucca filamentosa x Yucca gloriosa

Yucca X albella
Yucca X candida
Yucca X Engelmanii
Yucca X ensata
Yucca X floribunda
Yucca X margaritacea
Yucca X micans
Yucca X Moraea
Yucca X Parthenope
Yucca X preacox
Yucca X Rekowskiana
Yucca X robusta
Yucca X Triton
Yucca X Wilhelmi (Gugielmi)

Yucca filamentosa media x Yucca gloriosa

Yucca X bicolor
Yucca X elegantissima
Yucca X elmensis ('St. Elmo')

Yucca filamentosa x Yucca recurvifolia

Yucca X Aurora
Yucca X Ceres
Yucca X exsultans
Yucca X Federicus Cäsar
Yucca X Lachesis
Yucca X lanceolata
Yucca X Magnolia
Yucca X peregrina
Yucca X princeps
Yucca X viridiflora
Yucca X Willmottiana

Yucca filamentosa media x Yucca recurvifolia

Yucca X fulgens
Yucca X Imperator
Yucca X regia
Yucca X Sanderana
Yucca X victorialis
Yucca X Klotho
Yucca X Cybele
Yucca X imperialis
Yucca X Koelleana
Yucca X Milton
Yucca X Passiflora
Yucca X purpurascens
Yucca X Tenoreana
Yucca X Virgilius
Yucca X Wittmackiana

Yucca flaccida x  Yucca gloriosa longifolia

Yucca X luxurians

Yucca flaccida glaucescens x Yucca gloriosa

Yucca X Colombiana
Yucca X formosa
Yucca X formosissima
Yucca X nebularis

Yucca flaccida glaucescens x Yucca recurvifolia

Yucca X amabilis
Yucca X campanulata
Yucca X caelestis
Yucca 'Eros'
Yucca 'Flora'
Yucca 'Luna'
Yucca X grasilis

All of the above hybrids where described by Sprenger and all of them has flowered for him.

Besides the above hybrids did he also name some that he hasn't seen in flower those where:

Hybrids with Yucca treculeana canaliculata, recurvifolia and gloriosa
Yucca Athene
Yucca Fredrich der Grosse
Yucca Thusnelda

Hybrids with Yucca flaccida,  Yucca filamentosa, Yucca recurvifolia and Yucca gloriosa

Yucca Albatros
Yucca Astra
Yucca Comesii
Yucca Delpinoana
Yucca falcata
Yucca hystrix
Yucca pulchra

Reference:

Sprenger, Carl., Mitteilungen Deutschen Dendrol. Gesell. 29: 96-138 + pls.: 21-22. (1920)
Mitteilungen über meine Yucca-Hybriden und -Formen, gezüchtet in den Jahren 1897-1907.

Notes:
It should be noticed that Sprenger's article were published in 1920, 3 years after his death in 1917.

In the article mentioned above Sprenger that he also made hybrids with Yucca schottii, but it seems as he did sell all the plants as seedlings, and did not grow any to bloom, so no specimens were given a name. Those hybrids with this seed parent were most likely made and sown sometime between 1870-1890.

He mention a Yucca schottii x flaccida on page 113. So he did  at least made hybrids with this "parenthood". When Sprenger did write the above shortly before his death in 1917 he did know of a plant in Napoli, Italy, which he believed to be this hybrid.

Unfortunately were many of Sprenger's plants destroyed by volcanic ash when Vesuvius erupted in 1906.

Only few is known to be in cultivation:

Yucca 'Vittorio Emanuele II'
Yucca 'Floribunda'
Yucca 'Elegantissima'

It is possible that there more "out there", but the above three is the only forms which I know of. Sprenger did also sell many unnamed hybrid-seedlings, and is very possible that some of those is growing in different places around the Mediterranean or on Corfu on which he lived from 1907 until his death 1917. 

If any of the readers know of any beautiful Yucca plant in this area of Italy, I am most interested in seeing photos and receive a small cutting of it.

Read more about Sprenger on answers.com