Incorporating liquid crystal (LC) as a defect layer in a photonic crystal (PC) leads to the electrically tunable optical spectrum in defect modes within the photonic band gap. While the LC defect layer has bi- or multi-stable states, the profile of defect modes in each stable state can be preserved permanently without applied voltage, indicating a feature of low power consumption for photonic applications. In this paper, we report on our recent development of optical and spectral properties of multilayer PC structures containing various types of memory-enabling LC (ME-LC), including a bistable chiral-tilted homeotropic nematic (BHN), a bistable chiral-splay nematic (BCSN), a bistable dual-frequency cholesteric LC (DFCLC), a tristable polymer-stabilized cholesteric texture (PSCT), and a tristable smectic-A liquid crystal as a defect layer. The defect modes of the PC/ME-LC cell can be switched to not only the voltage-sustained states but the memory states. As a result, PC/ME-LC cells reveal several features such as the wavelength tunability, transmission tunability and optical bistability or tristability of defect modes that are of potential for realizing tunable and memorable optical devices such as low-power-consumption multichannel filters, light shutters or electrically controllable intensity modulators with green concept.