Data for the conductivity, kappa, of selected binary mixtures of the ionic liquids [emim][BF(4)], [bmim][BF(4)], [bmim][PF(6)], [bmim][DCA], and [hmim][BF(4)] with polar solvents (water, propylene carbonate, dimethylsulfoxide, methanol, dichloromethane) at 25 degrees C are reported. Additionally, mixture densities, rho, were determined to convert kappa into molar conductivity, Lambda. The obtained results were fitted by appropriate interpolation formulas. Where possible, data were compared with information from the literature. Electrode polarization and sample purity, including [BF(4)(-)] hydrolysis, were considered as possible sources of errors in kappa. The effect of viscosity on the accuracy of rho and thus Lambda was checked.