Demeter Janakidisz is working at the Botanical Garden in Budapest, Hungary. In the botanical garden he have made some very special Yucca hybrids:

Yucca aloifolia x arkansana.
Yucca aloifolia x baileyi.
Yucca aloifolia x  filamentosa.
Yucca aloifolia x elata.
Yucca aloifolia x glauca ssp. stricta.
Yucca aloifolia x recurvifolia.
Yucca (aloifolia x elata) x baccata
Yucca angustissima x arkansana.
Yucca arkansana x angustissima.
Yucca baileyi x gloriosa.
Yucca baileyi x recurvifolia.
Yucca baileyi x stricta.
Yucca baileyi x ? (gloriosa or recurvifolia or neomexicana?)
Yucca glauca ssp. stricta x recurvifolia.
Yucca glauca ssp. stricta x baccata.
Yucca gloriosa forma robusta x elata, made together with Ferenc Kurilla.

You can read more about the hybrids on this Hungarian website (Text in English).

Photos of some of the hybrids:
 

Yucca aloifolia x filamentosa This plant is very much similar to Yucca gloriosa Copyright 2008 Demeter Janakidisz	Yucca aloifolia x filamentosa This plant is very much similar to Yucca gloriosa Copyright 2008 Demeter Janakidisz	Yucca aloifolia x filamentosa This plant is very much similar to Yucca gloriosa Copyright 2008 Demeter Janakidisz	Yucca aloifolia x filamentosa This plant is very much similar to Yucca gloriosa Copyright 2008 Demeter Janakidisz
Yucca aloifolia x elata Copyright 2008 Demeter Janakidisz	Yucca aloifolia x elata Copyright 2008 Demeter Janakidisz	Yucca aloifolia x elata Copyright 2008 Demeter Janakidisz Later this year the two Yuccas in the picture bloomed and Demeter were able to pollinate the Yucca aloifolia x elata with the Yucca baccata.
Yucca aloifolia x glauca ssp. stricta Copyright 2008 Demeter Janakidisziz	Yucca aloifolia x glauca ssp. stricta Copyright 2008 Demeter Janakidisziz