If you liked the Ergo Proxy anime, the Anime-Planet community thinks you'd like:
In a world where corporations snuff out the competition by sending fighter jets to attack their offices, teenage pilot Kannami Yuichi is reassigned to a new base. There, he meets Tokino, a carefree pilot who enjoys the company of older women, and Kasanagi Suito, his superior officer who he slowly falls for. However, not everything is as it seems. Soon, distressing questions are raised about Kannami's predecessor, a race of perpetual adolescents known as the Kildren, and the enemy ace of the skies, Teacher.
Well, both of these anime(s?) deal with the human condition as a whole, and the existential crisis in particular.
In both anime(s?, again), the main view point is that the ad hoc raison d'erte of the average human is determined by the role he is given in society by "the powers that be".
In Ergo Proxy, we see manifestations of those powers in the Regent and the Council, and, ultimately, Proxy One. Proxy One is also a hint to the idea of Free Will, but to save the spoilers, I won't ellaborate on that.
In Sky Crawlers, these powers are mainly the government.
The main difference between the stand points of the two anime(s? once more) is that while Sky Crawlers maintains that the human condition is a closed circle of events, and existence itself will keep it's balance by replacing rogue peons should they try and break free, Ergo Proxy claims that each individual has the power to challenge the status quo of the world.
Ten years have passed since the demise of the bubble economy, a time that polarized the world into two groups of people: the rich and the poor. In the present day, Saiga Tatsumi (a former war photographer) has been hired to investigate a secret club for the rich named the Roppongi Club, but he soon discovers secrets much darker than he’d ever imagined. With the help of a exploited goddess named Kagura, Saiga now possesses the power to kill by simply taking a photograph; but can he stay alive long enough to save her from her captors?
Both are darker series, both in unique animation style and plot lines. Speed Grapher and Erog Proxy also both feature very abstract, futuristic and apocalyptic worlds. Also, both are similar in that the protagonists are slightly jaded and trying to survive with their newfound knowledge. Raging against the machine and all that.
The eccentric mad scientist Okabe, his childhood friend Mayuri, and the otaku hacker Daru have banded together to form the Future Gadget Research Laboratory, and spend their days in a ramshackle laboratory hanging out and occasionally attempting to invent incredible futuristic gadgets. However, their claymore is a hydrator and their hair dryer flips breakers, and the only invention that’s even remotely interesting is their Phone Microwave, which transforms bananas into oozing green gel. But when an experiment goes awry the gang discovers that the Phone Microwave can also send text messages to the past. And what's more, the words they send can affect the flow of time and have unforeseen, far-reaching consequences - consequences that Okabe may not be able to handle...
Steins;Gate and Ergo Proxy are alike in that they are both psychological and deal with inner conflict as well as memories. Ergo Proxy is a little more serious and very stylized while Steins;Gate is more comedic but still equally mind blowing.
In a world of science, sorcery is rediscovered and rapidly adopted in all areas of industry – but at a high price: an invisible pollution is spreading out across the world. Those who do not take proper precautions become infected, lose their sanity, and become demons. The Sorcery Administration Bureau, along with their Tactical Sorcerers, monitor magic uses and respond to any demonic outbreaks that occur. In this world, Ray Otto is a rogue tactical sorcerer who hunts down demons with reckless abandon. Given that he always gets the job done, the administration generally lets his activities slide. Together with the mysterious girl Kapel Theta, Ray risks his life and humanity to destroy demonkind... when the price is right.
Both series are about characters that are trying to find themselves. With Ergo Proxy you have Vincent trying to figure out and then finally accept who he really is after a long journey of self-discovery.
While you have Ray in a constant struggle to not only to rid the world of demons but slowly loses himself and risks becoming that which he hunts.
Forty years ago the citizens of Paradigm lost all of their memories, and live their lives without any knowledge of their past, or any hope for the future. Roger Smith is a man who performs the much needed task of negotiator in Paradigm. He provides his services to the wealthy with the help of a peculiar android named Dorothy and his mechanically inclined butler Norman. When greater evil arises, he calls on his magnificent relic of Paradigm's past, the Megadeus Big O. With Big O at his side, Roger Smith may be Paradigm's only hope of surviving in this new world without memories.
The Big O and Ergo Proxy have almost nothing in common, besides a similar setting. They both take place inside of large, futuristic cities, protected from the otuside world by large domes. If this is a theme you enjoy in anime, you would enjoy watching these.