Total Recommendations: 3
Katanagatari and Spice and Wolf have similar pacing, and are both extremely dialogue-heavy, especially between the two main characters. Both have a fantasy-type setting, but Katanagatari also has some action scenes, while Spice and Wolf revolves around merchants and trading. If you enjoyed the character interaction between the characters of one of these shows, you will probably like the other as well.
It is impossible to say that Darker than Black (specifically the first season of DtB) and Phantom: Requiem of the Phantom are not similar, especially the characters. Hei and Zwei are both assassins who work for an organisation they don't really know much about; while Yin and Ein both start out seemingly emotionless but undergo significant character development throughout the series. If you liked one, it is very likely you will enjoy the other one as well.
Angel Beats! and Haibane Renmei have similar concepts, as both are centered around characters who are in a purgatory-like setting. While Angel Beats! has more comedy and action, Haibane Renmei takes a much more serious tone, and also likes to leave things up to the viewer to interpret. Liking one of these shows does not necessarily mean you will like the other, but it is worth trying.