As the semiconductor technology continues its marching toward the deep sub-micron domain, the strong relation between leakage current and temperature becomes critical in power-aware and thermal-aware design for electronic systems. Previous circuit-level research results can capture the leakage/temperature dependency accurately, but can be too complex and thus ineffective in high level system design. In this paper, we study a large spectrum of leakage power models that are able to account for the leakage/temperature dependency, and in the meantime, are simple enough and suitable for system level design. We analyze and compare the tradeoff between the complexity and accuracy of these models empirically. Our experimental results strengthen the important role that the leakage power consumption plays in the electronic system design as the transistor size continues to shrink. More importantly, our results highlight the fact that it is vital to take the leakage/temperature and leakage/supply voltage dependency into considerations for high level power and thermal aware system level design.