Oh gosh, that is such a hard question...
Studio Ghilbli, Studio Ghibli, Studio Ghibli.
I'm currently very obsessed with the openings and ending songs from FMAB. The animation sequences of course help with it, too.
AoT- absolute awesome, enough said. Same goes for Cowboy Bebop.
Madoka has been mentioned here. I absolutely adore the ending (the second one) of the anime and consider it as one of the best anime ending songs of 2011. Two other tracks are also very special to me:
Then there is Tokyo Ghoul. Yes, the anime was kitten, but I can't help but listen to certain tracks over and over again. Unravel is still number on opening for me from 2014. I don't care if people think it is overrated XD And I love the ending song of season 2.
Code Geass has a phenomenal soundtrack if you ask me.
Early German openings from Pokemon and Digimon, too ^^
@Nar123, I love that one track from Hitman Reborn
... This became way too long, lol.