Well, when it comes to "peaceful" anime, slice-of-life and comedy instantly pop up to mind. With that said, here are some of what I'm gonna recommend:
Comedy:
Full Metal Panic? Fumoffu
Bamboo Blade
Seto no Hanayome
Slice-of-life - has simple plots, and peaceful, some may feel boring.
Minami-ke
Lucky Star (first 4 episodes pretty boring though, but I like the ones after it)
[The above two are pretty funny and interesting as well]
I haven't watch Haibane Renmei so I actually don't know what you are looking for, or if I understand what you mean by 'peaceful' correctly. If you mean something that has this surrealistic 'feel' to it then:
ef - a tale of memories
I'm an ALIEN!!!! - officially identified as by Konnichiwa 
Of course... My English is still... horrible - appreciation and thanks to FJ-Warez 
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