The University of Kansas also has a great guide for resources to use with studying kuzushiji. And if you're not already on the Minna de Honkoku みんなで翻刻 platform, please check it out right away too (plus read up on the history of the project and the related KuLA app in this DHQ article). You can find the old English intro page for Honkoku.org here which includes links to the YouTube intro videos and more.
These sites provide kuzushiji and hentaigana reference, such as charts and guides to be used by those who have already learned some kuzushiji and hentaigana.
These are more comprehensive dictionaries of kuzushiji, hentaigana, and calligraphic kanji forms.
These digital archives contain page images of documents written in kuzushiji with hentaigana and kanji, and many also include honkoku 翻刻 that can be viewed alongside or superimposed on the original documents.
Other digital archives which contain materials relevant to kuzushiji and hentaigana reading, but not necessarily images of texts and/or honkoku.
These sites and other resources provide tutorials and guides on learning kuzushiji in a structured way, rather than just serving as reference tools.
These are sites with information about premodern books, or kotenseki 古典籍.