Two new ionic liquids (ILs) with siloxane-functionalized cations and the weakly coordinating tetraalkoxyaluminate [Al(hfip)(4)](-) (hfip=hexafluoroisopropoxy) are prepared and characterized by nuclear magnetic resonance (NMR), infrared (IR) and Raman spectroscopy. With melting points below 0 °C they qualify as room temperature ILs (RTILs). Their temperature-dependent viscosities and conductivities, together with those of two [Tf(2)N](-) ILs with the same cations and a further siloxane-functionalized [Tf(2)N](-) IL, are measured between 0 and 80 °C, and all are described by the Vogel-Fulcher-Tammann (VFT) equations. We note that the [Al(hfip)(4)](-) ILs have lower viscosities than their [Tf(2)N](-) analogues at all measured temperatures and higher conductivities at room temperature.