Lamp

The Lamp is a... Lamp. Yeah.
Her first appearance was in the episode Space for Rent, where the Commander gets drunk on non-alcoholic beer and starts making out with a lamp. The lamp is later revealed to be sentient when she asks Psycom "but I thought you said that I was the only one for you?", apparently won over by Psycom's drunken advancements while impersonating the Commander.
She is seen as being in a relationship with the Commander in a 25-year flash-forward to the future in the episode Space Package, although The Commander's life-long obsession with a random package seems to putting strain on their relationship.
She appeared as a contestant in the special episode What's Inside That Tree? in which she is presented as a prize to the winner. In an easter egg at the end of the episode, Psycom jumps down in front of the lamp holding flowers and yells "Hell yeah!", implying he may still have romantic intentions towards the lamp.
Her last speaking appearance was in Desert Space, where the Commander presents her as his partner when speaking to the Christophers, however shortly after this he offers to trade her to them for a beer (in response to which she cries "I never loved you anyway!"). This is also the episode that confirms that the lamp is female, as the Commander presents her as "the lady", and when asked about this by the Christophers clarifies that "it's a female lamp". Why the Christophers aren't aware of this is unknown, as Christopher 1 can be seen putting the moves on Lamp at Ghost Spider's party in the previous episode.
In the episode Space Package one of the end credits is "db terjesen as "alice" ". Given that the lamp is the only female character in the episode, and the only one with a speaking part whose name we don't otherwise know, it seems to be implied that the lamp's name is actually Alice.