Well, I have two main animes that I go watch again and again. Isekai no Seikishi Monogatari and Heroic Age. I've lost count of how many times I've watched it.
There's also 12 Kingdoms and Dragon Ball that I occasionally go back to, also, Code Geass and some Gundams series. But isekai no seikishi monogatari and heroic age are great to watch over again cause of the characters, they're OP and they have really great personalities.
I also watched kore wa zombie desu few times, comedy can be fun to re-watch.
Any recommendation? Maybe I missed something.