I've bought and successfully tested 4 kinds of USB devices under Windows 98 (8 megabyte installation, running with 32 megs of RAM) and they were all extremely cheap on EBay.
1. Sound cards (including microphone for voice recognition)
2. Video capture (4 camera inputs in realtime while running Vault-OS Web server)
3. IrDA dongle (transmit anything with infrared, including over optical cabling)
4. USB Dotmatrix printer (never needs ink ribbon, for printing barcodes)
You might be amazed to discover that these devices still commonly have Windows 98 drivers. I was.
This is just a heads up to invest in these cheap little peripherals while they still support the Windows 98 operating system. Some of them are $5.00-$10.00 on EBay with free shipping.
Not known yet if you can use these USB devices when running Win 98 in "No-GUI" console mode. Testing is forthcoming.
Note the IrDA is very useful in situations where you want to run an EMP proof line somewhere, like an optical fiber to a weather station or security camera aboveground.