A set of telling time (to the hour) flashcards. I like these because they list the dignital time (such as 1:00) right under the picture of a clock showing that time. I believe it was Temple Grandin who recommends that flash cards for students with autism include the term on the same side as the picture, to help make the connection.
The flashcards from from AdaptiveWorksheets.com .
My Book of Telling Time (Kumon Workbooks)
I'm not generally a huge fan of workbooks, but the Kumon series has worked very well for my students.