…and I can’t remember who it was! I think the request came via WordPress, but I’ve gone back through my comments and I can’t find it.
In any case, mystery person, if you liked Anna Karenina, here’s where you can go from there:
To other European adultery novels
The two most famous are Madame Bovary, by Gustave Flaubert, and the slightly less well-known Effi Briest, by Thedor Fontane. Madame Bovary is, as I recall, mildly infuriating because Emma Bovary is so bloody difficult; Effi Briest, on the other hand, is short and totally fascinating because it has so much to say about the idea of “Prussian rectitude” and how silly and destructive it is to live your life by an overarching patriotic standard that has no room to accommodate the needs and wishes of the individual. Also, Effi is a terrific heroine. She’s calm and composed throughout, even in her final illness, and although she dies (of course), her husband actually dies first, which, in the context of an adultery novel, basically means she wins.
To other novels about the Russian aristocracy
I’ve not read very much Russian literature, but try Ivan Turgenev’s Fathers and Sons for further depictions of young men trying to implement political and agricultural reforms against the prejudices of their elders (like Levin in Anna Karenina). There’s also Boris Pasternak’s Doctor Zhivago, which will deliver a similar sort of sweeping love story. (Bonus: you can watch Keira Knightley starring in the films of both Doctor Z. and Anna Karenina, and decide whether you’re more convinced by her Lara or her Anna. Or neither.)
To more Tolstoy
You can read War and Peace, obviously, if you like. I’d recommend making some sort of chart for the characters, though. He also wrote a novella called The Kreutzer Sonata, which I bought for $3 from a secondhand bookshop in Maine when I was fifteen because I’d heard it referred to as a “disturbing psychosexual drama”. It was less dirty than I had been hoping, but it’s got the whole passion/death complex that Anna Karenina has in spades.
I hope this finds whoever asked me about it…terribly sorry for forgetting the circumstances/identity of the questioner!
Elle Thinks 
I am not a big fan of Anna Karenina. I liked it, but didn’t love it. Same with Madame Bovary, although I liked this one a bit better because I found it more amusing, not quite as serious. I think it’s partly because it drives me crazy that these women having affairs have to suffer in some way. All of this to say that I am happy to hear about Effi Briest and have added it to the list! Yay for women not going crazy or committing suicide!
I also really like how her adultery isn’t a passionate affair so much as it is Effi getting a bit bored. Her hubby doesn’t even find about it for *literally years* and then completely flips out, which makes him look a bit irrational. Haha.
It’s true! To outlive your husband in a European adultery novel is a startling win! I have read Effi Briest, and I remember I loved it, but it was soooo long ago now that I can’t recall the details. I remember Effi entering a room and ripping her bodice off in a gesture that symbolised the intolerable repression of her culture. Yup, definitely a great novel!
It’s ace, no?! She’s pretty cool. It also has the inestimable virtue of being short.