Mouse and Keyboard
Any USB mouse and keyboard that did not require standalone drivers would work with the PS2 USB ports. The PS2 lacked an official web browser, limiting the mouse and keyboard usage to any online games that supported them.
Compatible devices
Other devices utilized by the USB ports included the PS2 Multitap, which allowed up to 10 players on the PS2 simultaneously. The EyeToy, the PS2's official webcam/microphone, also utilized the USB port.
Incompatible devices
While USB Flash drives fit into the USB ports, they would not work. USB Flash drives couldn't be used to save game data or transfer data between consoles. Phones, MP3 players and other devices that are compatible with newer consoles would not work with the USB ports on the PS2.