It’s been a couple years since there’s a thread like this, as far as I can tell…
All the Lois McMaster Bujold Vorkosigan-verse books. I’ve read all at least three times, and we’ve purchased (in one form or another) most of them more than once.
Harry Potter, of course - both as they came out (e.g. when 5 came out, I re-read 1-4), but periodically since then. Right now I’m slogging through book 1 in French (made much easier by purchasing a dictionary for my Kindle). Knowing what’s going on helps me figure out what’s happening when I don’t quite get the idiom being used. Plus hey, I’d much rather be a Moldu (Moldue? the book isn’t clear whether one should feminize the noun) than a Muggle :D.
Some classic SF - have read most of Heinlein at least twice and even sprung for the audiobook of The Moon Is A Harsh Mistress.