the first sci-fi that I reeeaaally liked Steins;Gate one of the decent shounen fantasy that I liked Fairy Tail
Ore no Imouto Amagami SS
Kaichou wa maid-sama Kimi ni Todoke
Ao no Exorcist Kuroshitsuji and all the angel-devil related
I sometimes base and rate the animes that I soon to like on the quality. like how the background looks so realistic but it's obviously from anime (excluding kaichou wa, I liked the story over quality) and the choice of seiyuuuus.
Clannad After Story, Mahou Shoujo Madoka★Magica Higashi No Eden (Eden Of The East) Toki wo Kakeru Shoujo (The Girl Who Leaped Through Time) AnoHana (Ano Hi Mita Hana no Namae wo Bokutachi wa Mada Shiranai) Kanon(2006) Kaiji: Hakairoku Full Metal Alchemist: Brotherhood
These are my favorites ^_^ There are plenty more that I love, but these are the best!
Code Geass Katekyo Hitman Reborn Gundam Sekai-ichii Hatsukoi 07 Ghost Ayashi no Ceres Mawaru Penguindrum Black Lagoon All the anime from Key except for Air cause I didn't really like that one Wolf's Rain
etc.....basically whatever had a good story and kept me interested throughout are my favs I just don't want to list them all too lazy.