Marion Cotillard played the role of Edith Piaf in the 2007 biopic La Vie en Rose. The ever important song No, Je Ne Regrette Rien (sung by Edith Piaf) was almost cut from Inception by Nolan to avoid the unintentional casting coincidence, but Hans Zimmer convinced him to keep it. (Source)

Ariadne's final maze solution is circular, just like the classic depiction of Minos' Labyrinth (check out our "Names" in the Characterization Section for more info). (Source)

If you listen closely to James in the last scene, he tells his father that they are "building a house on a cliff." While Nolan says not to read too much into the improvisation of child actors, it's hard not to wonder at the significance of this line in relation to Limbo and the architecture motif as a whole. What do you think? (Source)

The Nolans' production company, Syncopy, has a very similar, maze-like logo to Inception. In fact, Syncopy comes from "syncope" which can mean "a brief loss of consciousness." This is apt not only for Inception but for many of Nolan's movies. (Source)