Dahons
Just be very very sure you are getting a model in which the handlebars are removable. I know that would seem obvious for a folding bike but it is not. I bought my wife an Espresso and found out the hard way the handlebars are not removable (my dumb). She would only ever put it in a van or trunk so she is okay with this. When it came time for me to get a new bike I got the Dahon Jack. It is seven speed which I can live with.
Those are 26" - I assume you want 20". I think this is less an issue with the 20 inchers because the handlebars usually fold, but be sure.
I used to own a Bazooka and I love how the handlebars unscrew without any tools, and how in the folded position the handlebars screw into a shaft in the frame that keeps the bike in a folded position. Plus the handlebars are not loose like on a Dahon.
If you're near Chicago check out Rapid Transit Cycle Shop on North Avenue - they have every folding bike imaginable in their show room, even Bike Friday and Strida. Strida is best if you want small though they admit it is not a bike for long distance trips. Even so it is my fantasy to own one someday, just an incredible piece of engineering.