The BBx is arguably the most important concept, though the one that garnered the most attention in recent years was the original FR-S (the "Friggin' Really Sweet" car) from the 2011 New York show. That came to production as Scion's (and Toyota's) best-driving car, using a lightweight, rear-wheel-drive architecture shared with the Subaru BRZ. Thankfully, the Scion FR-S will live on as the Toyota 86.
Also of note are the 2004 FiveAxie Speedster xA, 2009 Kogi BBQ Truck XD, original 2009 iQ concept (remember the iQ?), and a 2014 tC designed by Slayer. They're all on display here in New York, and you can see them all, one last time, in the gallery above.