The soundtrack for Haibane Renmei was truly wonderful.
I was really impressed with the soundtrack by Steins;Gate because I was unfamiliar with the two composers behind it. After checking, they've done very little prior to this, so here's to hoping they'll offer more of the same in the future.
I can't really remember the soundtrack for Red Garden, if I'm honest. I just remember the characters going into song unexpectedly, but it was rather enchanting.
I've bought the soundtrack for Shiki as I really like Yasuharu Takanashi's work, especially for Naruto Shuppuden but most recently for Log Horizon.