The VM6R offers multiple layouts and can be ordered as a case or preassembled. It also features both Iris and Lolli tech.
Chibico by Acrycade Gear is a mini stickless controller that should be able to fit into a back pocket of a pair of pants.
The Joytron EX Revolution Air is most recommended for Tekken players who'd like to enjoy playing wirelessly.
The Hori Fighting Stick Mini is an average mini fightstick that might catch your eye in the sea of competitors.
The FightBox R1-F is a dream come true for platform fighter players who love the Frame1 layout but would rather enjoy it with Sanwa buttons.
The QRD Maestro S3 can either work wirelessly or with a wired connection, depending on your preference when you play.
The Skullbox Leverless Arcade Controller is smaller & thinner than average and has proprietary SkullCaps that mimic the Sanwa feel.
You can buy the Qanba 2009 for one or two players, and you can also buy it with or without an arcade cabinet base.