Dice Cubes are an old and obvious sticker mod; a set of stickers, such that each one is a die face. As of November 2017, there are two available; one giving western-style dice from Olivér's Stickers, and one giving Chinese-style dice from the HK Now Store.
Unfortunately, the HK Now Store has discontinued their dice sticker set. It is hoped that Olivér's will pick up the rights and continue the supply of these.
There are also magnetic dice cubes available, these are supplied by magneticcube.com and are hand-made, hence very expensive compared to other cubes of the same size and order.