The set 40172 desk calendar has cubes for the day and month.
I had a spare set, so I thought it would be fun to add cubes for the day of week. All the days of the week can be represented (in English) with two cubes. The first cube has the letters M/W, T, F and S, and the second cube has O, U, E, H, R and A, which covers the first two letters of every weekday. This might not be easy to do on two cubes in some languages.
Desk Calendar Extension by James Shields, on Flickr