Anime you can't get out of the effect for a while.

k-on. Purely because of how wholesome it was. It had me wishing that I could have a life like that and stuff it was so perfect.

Kamichu and Dennou Coil. For a while, I was quite desperate to find something with similar aesthetics.

There are many but I will name one Baccano!

@Spast1c I'm thinking of watching k-on in free my time.

Flowers of Evil is a recent one which made me think for the whole week after watching it.
Also binged the rest of the story / manga the next day.

Lots, usually because of dramatic moments, like the ending of Rose of Versailles or Revolutionary Girl Utena. Also Girls Last Tour because of the melancholic vibe which makes you think. The shows of Aria franchise for the soft relaxing vibe which come mind every time the ocean breeze blows softly over the estuary, or One Piece every time the palm tree in the garden waves in a stiff wind framed against a bright blue sky with seagulls wheeling about in the air.

Also some of the older classics like Ashita no Joe S2, that ending is brilliant, packs a punch. And ofc LotGH, it's a masterpiece, no other grand stories compare.

For me it would be Aikatsu. I can't help to keep listening to their songs. I never fond of any idol anime at all but this one just hits different because of how complete it made me feel be its highs and lows. Binging the franchise up to Parade in just 2 months is surely a session that I would not forget.