USB Drivers Included with Windows
These are the USB drivers I'm aware of that were added to each edition of Windows. Except as noted, the newer editions have all of the drivers from the previous editions.
Details about the drivers are available at Windows Hardware and Driver Central, the Windows DDK/MSDN documentation, and in the example code provided with the DDKs. I've eliminated most of the direct links to Microsoft's documentation because the URLs change frequently. A search on the listed topic should point you to relevant pages. Also useful are the class specifications available from the USB Implementers Forum.
Windows 98 Gold (original)
Drivers: usbaudio.sys, wdmaud.sys, wdmaud.drv
Audio Drivers (MSDN Library)
Audio /Speech Technologies (Windows Hardware and Driver Central)
DirectX (for DirectSound and DirectMusic)
Includes keyboard, pointing devices.
Documentation: see Windows 98 SE below.
USB camera minidriver library (USBCAMD 1.0)
Not supported under Windows 2000.
Documentation: see Windows ME below.
Windows 98 SE
HID 1.1 (adds the ability to do interrupt OUT transfers)
Drivers: hidusb.sys, hidclass.sys, hidparse.sys
Communications (modem, virtual COM port)
Drivers: usbser.sys, ccport.sys
Modem Devices (MSDN Library)
Modem - Architecture and Driver Support (Windows Hardware and Driver Central)
A fix for a problem with usbser.sys (from Microsoft).
Still image capture
Scanner, camera (first phase/preliminary)
Documentation: see Windows ME below
Driver: usbstor.sys. Support for multiple LUNs (partitions) added in SP3.
Storage Devices (MSDN Library)
Storage - Architecture and Driver Support (Windows Hardware and Driver Central)
The T10 Technical Committee is the source for the SCSI standards the driver is based on.
The Mass Storage Page.
Printing - Architecture and Driver Support (Windows Hardware and Driver Central)
Display and Print Devices (MSDN Library).
Until Microsoft ends support for Windows 98, the printer driver is allowed to be distributed for use on Windows 98 systems.
Communications (Remote NDIS)
Remote NDIS is the Network Device Interface Specification used for USB/Ethernet adapters.
Remote NDIS Communication (Windows Hardware Dev Center)
Network Devices and Protocols (MSDN Library)
Smart Card/Chip Card Interface Devices
This driver (Usbccid.sys) isn't included with Windows, but is available for Windows 2000 and later editions via Windows update.
Microsoft Class Drivers for USB CCID Smart Cards (Windows Hardware and Driver Central)
MIDI (in the Audio driver)
Reports are that the MIDI support is greatly improved in Windows XP.
Still image capture
Scanner, camera (much improved)
Still Imaging / WIA Technologies (Windows Hardware and Driver Central)
Windows Image Acquisition (WIA) (MSDN Library)
Still Image Devices (MSDN Library)
Video (also see Windows XP below)
USB camera minidriver library (USBCAMD 2.0)
Streaming Devices (Video and Audio) (MSDN Library)
DIrectX Developer Center (for DirectShow)
Added in SP1. Bthusb.sys.
Wireless Network Technologies (Windows Hardware and Driver Central).
Added in SP2. This driver doesn't require a vendor-provided minidriver.
USB Video Class Driver Overview (MSDN Library).
Communication (Wireless Mobile Class)
Support for the Wireless Mobile Communication Device Class (WMCDC) (MSDN Library)
Supported USB Classes. From Microsoft.
USB FAQ: Introductory Level includes a chart of drivers and OS editions. From Microsoft.