Roy Sakuma created and offers a nice chord chart that groups chords by progressions within keys.
For example: In the key of C he put the following chords:
i = C | vi = Am | iv = F | V7 = G7 | iii = Em | ii7 = Dm7
This is a great way to practice chords.
Click here for the whole chart!
TinyCards.com (from DuoLingo.com) is a great tool for creating flashcards. You can save the individual chords from UkuleleGo.com and paste them into the flashcard maker. Here is an example I created.
Ukulele Chord Cubes would be great to use like dice or something like that. Here are some sold by Ukulele Magazine.