Mercury
Mercury is a small rocky planet in the inner solar system. As Mercury is deep in the Sun's gravity well, the energy to move materials from Mercury to Mars is very high. Reaching low orbit from the surface requires 3km/second in high thrust v, with another ~9km/second required to reach Earth or Mars[1][2]. This v can be made utilising electric propulation however, as it has much lower thrust requirements. Mercury could eventually serve as a source of power for the solar system, as the solar flux at the surface is very high at 5-10x the amount of energy from the sun per square meter[3]. Beamed power could be sent to other planets in the solar system from Mercury's surface, although this might best be achieved using solar orbital power stations.
If mass drivers ever become common in the solar system, making the energy to transfer material from one gravity well to another a trivial cost, Mercury might serve as a mining resource. It has a very high density, and material from the core might be more easily accessible than for other planets.
Similar to the moon, it has a metal rich regolith along with what appears to be permanently shaded regions at the poles that may harbor water or possibly other volatiles[4]. As such some have discussed the colonization of Mercury[5].BepiColombo, due to reach Mercury in 2025 will provide more detailed observations of the planet.
