Schnapsen (pagat, WP) - a 2p trick-taking game playable with a standard or German suite deck. A unique aspect of it is that the trick-taking rules change mid-round. In the first half you can don't have to follow suit at all, you can play whatever you want. When the draw-deck runs out or when one of the players decides to "close" the deck the rules change and you must follow suit or play trumps. The timing decision of when to "close the deck" is a really cool one and it's what makes the game.
Regicide - is a co-op (or solo) that does a really good job at giving a varied game experience with a standard deck.
Haggis - a ladder-climbing game that's playalbe with a standard deck with 2 players. Needs custom deck for 3.

Other:

Mottainai - An amazing amount of game in a 54 card deck. Probably my overall favorite card game
Sea Salt & Paper - Very addictive, especially on BGA. It sort of a set collection game with rummy-style hand management that includes some cool abilities you get when you get the right pair of cards.
Love deckbuilders in general. Overall favorite is probably Ascension but also love Star Realms, Clank, Dominion etc. Happy to play pretty much any deckbuilder anytime.
For Northwood - a solo tricktaker. How does that even work? Very well as it turns out! Excellent art and production too.
SCOUT - another climbing game that works well at 2p
Honorary mention to Hats which is this week's favorite. Has some of that Arboretum meanness but plays very differently. It has a card flow that took a while to get used to but very neat once we figured it out.