An EXT port is often a USB-A port where you can insert an adapter, converter, or dongle and make your controller compatible with more consoles.
This Perfect Clear controller supports MX switches from GamaKay to Akko as well as a PCB like the Brook Fusion.
The elegant Punk Workshop Leverless M has a size that is comparable to that of a tablet device, but that is only one of its many features...
JumpHack is one of Japan's finest sources of highly customizable controllers, such as the JumpHack11-XL (also known as the JH11XL).
The Studio is so customizable that—in addition to its layout—you can pick the colors of its buttons' rims.
The X8 is PXN's debut WASD-style controller that sports some interesting artwork which is refreshing to see.
In addition to a Sanwa joystick, you can order the Joytron EX Revolution with a Crown lever variant of your choice.
The Taito Egret II Mini Control Panel can be used with the Egret II Mini arcade cabinet or as a PC arcade stick (with the proper drivers).
Ultra Arcade's Standard series is a reasonable entry point into its customizable controllers, and there are Pro & Lite editions available.