In addition to many of the games listed here, also consider:
* Deep Sea Adventure — A tiny push-your-luck game that blends theme and mechanics perfectly, is easy to explain, and is a ton of fun without being too thinky. It also scales perfectly from 2 to 6 people. Expensive if you're just counting components, but the value of the game and the fun it brings makes it worthwhile.
* Celestia — Also push-your-luck style, but with a bit more production (and, oddly, cheaper than Deep Sea Adventure).
* Patchwork — A great little two-player game where you're making a quilt. That sounds silly, but it's like Tetris that's powering a small economical engine. Really fun.
* For Sale — Good for 3-6 players, a really simple little card game where you get properties in the first round and auction them off in the second. Plays in 15 minutes, fits in a small box. (I think they even make a travel version.)
* Santorini — the retail version is a big production, but if you get it, you could easily make a smaller version of it. Takes 30 seconds to learn and is hard to really master. Comes with a ton of God power cards that make a bunch of replayability.
* Smash Up — the base set comes with 8 factions. Each player takes two factions (of their choice, at random, etc.) and smashed them into a deck. You then compete against others to topple bases and score points. A lot of fun with the right crowd. I think they've released about 50 factions total so far, with 8 new ones released each year currently. All totally optional.
* Star Realms — great little two-player deck builder. It's space themed, if you want another theme, they have other versions that work similarly. It's just one deck of cards, plus expansions if you like it.
* Dixit — I love Dixit. I've never played it with anyone that didn't have fun. The box really spreads things out, and is mostly holding the scoring track, but you could replace that with something smaller easily. A deck of amazing art cards, a couple of voting tokens, and a way to keep score. Could fit into a sandwich bag if you create a smaller scoring system.
* Deep Sea Adventure — A tiny push-your-luck game that blends theme and mechanics perfectly, is easy to explain, and is a ton of fun without being too thinky. It also scales perfectly from 2 to 6 people. Expensive if you're just counting components, but the value of the game and the fun it brings makes it worthwhile.
* Celestia — Also push-your-luck style, but with a bit more production (and, oddly, cheaper than Deep Sea Adventure).
* Patchwork — A great little two-player game where you're making a quilt. That sounds silly, but it's like Tetris that's powering a small economical engine. Really fun.
* For Sale — Good for 3-6 players, a really simple little card game where you get properties in the first round and auction them off in the second. Plays in 15 minutes, fits in a small box. (I think they even make a travel version.)
* Santorini — the retail version is a big production, but if you get it, you could easily make a smaller version of it. Takes 30 seconds to learn and is hard to really master. Comes with a ton of God power cards that make a bunch of replayability.
* Smash Up — the base set comes with 8 factions. Each player takes two factions (of their choice, at random, etc.) and smashed them into a deck. You then compete against others to topple bases and score points. A lot of fun with the right crowd. I think they've released about 50 factions total so far, with 8 new ones released each year currently. All totally optional.
* Star Realms — great little two-player deck builder. It's space themed, if you want another theme, they have other versions that work similarly. It's just one deck of cards, plus expansions if you like it.
* Dixit — I love Dixit. I've never played it with anyone that didn't have fun. The box really spreads things out, and is mostly holding the scoring track, but you could replace that with something smaller easily. A deck of amazing art cards, a couple of voting tokens, and a way to keep score. Could fit into a sandwich bag if you create a smaller scoring system.