In this paper we analyze and discuss the characteristics and expected benefits of some emerging device categories for ultra low power integrated circuits. First, we focus on two categories of sub-thermal subthreshold swing switches Tunnel FETs and Negative Capacitance (NC) FETs and evaluate their potential advantages for digital and analog design, compared to CMOS. Second, we investigate the combined low power and novel integrated functionality in some hybrid Nano-Electro-Mechanical (NEM) devices: the Resonant Body (RB) Fin FET for nW time reference ICs and dense arrays of Suspended Body (SB) Double Gate (DG) Carbon Nanotube (CNT) FET for low power analog/RF and integrated sensor arrays.