For 52 card, I’m a sucker for trick-taking. So games like Hearts and Spades. One of my friends has been importing a ton of small box games from Japan and Korea, and there are some good card games in the batch like Hachi Train and Nana (aka Trio).
Make sure to check out Schnapsen if you haven't already. Great choice when you only have 2 players. I have a little blurb and links in my other comment.