Card games
The Goofspiel Card Game and Golf and Oh Phooey and Whist and Bridge and Poker and Hearts and Spades and Spoons are all good games. Euchre and Napoleon are not quite so good. 500 Rummy might be added to my list.
Spoons is very good. Entertaining and hilarious. It can be played by from 3 to 100 people. It is unusual in how good it is even with large numbers. I've played it with 10, which worked very well.
Bridge
For three people, bridge with a dummy hand laid out with 8 cards showing and 5 concealed is fun. The three players bid for the contract, and the winner gets the dummy and plays against the other two. You can even use regular bridge scoring rules.
Other bridge-like games are Spades (spades is always trump), Whist (a card turned at the end is trump, no bidding), Hearts (Hearts is trump, very different scoring rules that include the Queen of Spades being a bad card to win in a trick), Napoleon (5-card bridge, sort of), and Oh, Phooey (You must win exactly what you bid, differnet number of cards per hand each round).
Pinochle
Pinochle is a game I thought had possibilities, but after playing it online at cardgames.io, a very good way to learn it, I regretfully put it aside. The rules could be easily improved and it might be very good. It is a bridgelike game in which two sets of partners try to win tricks, though only 10s, Kings, and Aces in Tricks count for points (plus winning the last trick). There is bidding, which is interesting because you start off with a base score, before tricks, depending on how many aces are in your hands, and runs, and things like that. Also, you and your partner trade 4 cards before tricktaking starts.
One easy improvement is to allow partners to bid up rather than saying a player must pass permanently if he passes once. Another is not to require you to take a trick if you can, which eliminates a lot of interesting tactics.
The deck is special: a double deck, but with only nines and up. And Tens beat Kings, which is odd-- another easy improvement to make.
It might be good to add points for "melds" based on cards in tricks taken. This would make it impossibly complicated, but that would add a sort of interesting randomness.
