If you liked
Ga-Rei
|
...then you might like
Zetsuen no Tempest
|
Both are supernatural apocalyptic stories, where the main antagonists are those who wish to restructure the world.
If you liked
D.Gray-man
|
...then you might like
Ao no Exorcist
|
D.Gray-man is another exorcist manga with similar ideas. For one both protagonists have obtained powers that they didn't wish for and both end up dedicating themselves to organisations in order to fight demons/akuma.
If you liked
Ga-Rei
|
...then you might like
Tokyo ESP
|
Being by the same author, Ga-rei and Tokyo ESP both share similarities with the plots - fantasy powers, apocalypse and a group of protagonists that need to save the world. Another rather evident similarity is the author adding in elements of romance in both these series that mix quite well with both of these manga.
If you liked
Claymore
|
...then you might like
Shingeki no Kyojin
|
Both of the series have similar artwork; dark, rougher with panel composition that isn't typically seen in shonen manga but seinen itself. Much like Claymore, Shingeki no Kyojin finds itself on the border of the shonen/seinen genres by being a dark fantasy story which doesn't shy away from multiple deaths, limb loss and gore.
If you liked
Eyeshield 21
|
...then you might like
Kuroko no Basket
|
Both have same styles of humour and "shonen sports moves" - questionable moves and techniques that attract shonen fans but are mostly likely impossible to do in real life. Both of them have a relatively similar storyline as well with the protagonist's team aiming for the top by defeating several incredibly strong opponents.