If you liked the Android Kikaider anime, the Anime-Planet community thinks you'd like:
Murao Mima has created a robot daughter named Key, but after raising her for a very short time, Mima dies, leaving behind cryptic messages telling Key how she can become human. Key must struggle alone to learn the harsh lessons of life and search for the 'key' to her own dream: the power of 30,000 friends to make her a real human girl.
I enjoyed Key considerably more than Kikaider, but both focus on a similar concept: a robot who has a soul (or wants to have one). If you like watching a robot come to terms with their own humanity, you'd enjoy either of these titles. Expect Key to be a lot darker, with a lot more character development.
Both animes have as a main character a robot who is searching to become a human, and they both follow their adventures in seeking the imposible to make it possible
Among the garbage dumped down from the mysterious aerial city of Zalem, a new life is found. Restored by a brilliant cyberneticist, a young girl named Gally struggles to find her own place in the world, to learn the extent of her own deadly abilities and to discover that which makes her truly human: love.
If you liked watching Jiro try to gain humanity, you'd enjoy Battle Angel Alita as well; its main character is also a robot who has no recollection of her past. Battle Angel Alita takes place in a more post-apocalyptic setting and in general is much better, so try it out!
Metropolis is a grand high-tech city-state populated by humans and robots alike. It is in these streets that Detective Shunsaku Ban and his sidekick Kenichi search for the rebel scientist Dr. Laughton who unbenounced to them, is developing a super android named Tima as a tool for the Duke of Metropolis. What starts out as a normal case turns into mayhem as the scientist is murdered, and the true plans of the Duke are finally revealed...
Though Metropolis and Kikaider do not share the same creator (even though Kikaider's designs are very similar to Tezuka's), they share a very similar tone and feel. In each anime, a robot struggles to come to grips with his humanity - and in each, there is a colorful cast of supporting characters to either help or attack our protagonist. If you liked one, the other should seem like second nature.
As London prepares for the first World Expo, the young Ray Steam receives a package containing the Steam Ball, a small and incredibly powerful engine containing hyper-pressurized steam. Developed by Ray’s father and grandfather in America under the supervision of (and funded by) the O’Hara Foundation, the Steam Ball could prove to be an asset to civilization or a great danger. But after Ray finds out that the Steam Ball must not fall into the O’Hara Foundation’s hands, he sets forth on a mission to keep the item safe and away from those who would use it to fuel a brutal war...
With their similar themes of technology and the morals we have to question and revise upon technology's advent, it seems clear that Kikaider and Steamboy are worth watching. Though Kikaider moves a bit more slowly than Steamboy, it goes into much deeper depth on defining the difference (or is it similarity?) between human and robot, and how we all relate.