If you liked
Mars
|
...then you might like
Torikagosou no Kyou mo Nemutai Juunin-tachi
|
Both have characters that are artists (Kira in Mars and Yusei in Birdcage) that have other characters pose for their work (Rei in Mars and Kizuna in Birdcage). Both also have a lot of drama and romance.
If you liked
Gunslinger Girl
|
...then you might like
Baccano!
|
Both involve the mafia and gratuitous violence. However, Baccano! is much lighter than the deeply disturbing Gunslinger Girl.
If you liked
Deep Love: Ayu no Monogatari
|
...then you might like
Watashitachi no Shiawase na Jikan
|
Both are tragic love stories based off of novels that will make you cry
If you liked
Romeo x Juliet
|
...then you might like
Eikoku Koi Monogatari Emma: Molders-hen
|
Forbidden romances, similar characters (Romeo=William, Hermione=Eleanor, Lord Montague=Viscount Campbell, etc.), both inspired by English stuff (Shakespeare plays and maids, respectively) and both really good drama-romances!
If you liked
Kumo no Mukou, Yakusoku no Basho
|
...then you might like
Evangelion Movie 1: Jo
|
Both involve machines, mysterious girls, warfare and themes of friendship/love and finding one's place in the world. They also have a similar feel at the end.
If you liked
Ookami to Koushinryou
|
...then you might like
Suzumiya Haruhi no Shoushitsu
|
Besides having very similar characters (Holo=Haruhi, Lawrence=Kyon), they have a similar feel and have both happy and very sad moments.