Two systems in thermal equilibrium with a third are in thermal equilibrium with each other. (Page 6, Zemansky, Heat and Thermodynamics, 5th ed.)
The quantity of energy supplied to any isolated system in the form of heat is equal to the work done by the system plus the change in internal energy of the system. (Page 194, Williams et al., Modern Physics, 1980 ed.)
It is not possible to construct an engine whose sole effect is the extraction of heat from a heat source at a single temperature and the conversion of this heat completely into mechanical work. (Page 202, Williams et al.)
By no finite series of processes is the absolute zero attainable. (Page 498, Zemansky.)
Note that the Second Law can also be stated as the Law of Entropy, viz., that in any natural process, the entropy of the universe increases.