Here is what shows up in /var/log/messages when you plug one in (RH8)

• Keyspan Single port USA-19QW

Sep 12 14:52:08 localhost kernel: usbserial.c: Keyspan USA19QW - (without firmware) converter now disconnected from ttyUSB0
Sep 12 14:52:09 localhost kernel: hub.c: USB new device connect on bus1/1/2, assigned device number 6
Sep 12 14:52:09 localhost kernel: usbserial.c: Keyspan USA19QW converter detected
Sep 12 14:52:09 localhost kernel: usbserial.c: Keyspan USA19QW converter now attached to ttyUSB0 (or usb/tts/0 for devfs)
Sep 12 14:52:11 localhost /etc/hotplug/usb.agent: ... no modules for USB product 6cd/118/8001
Sep 12 14:52:12 localhost /etc/hotplug/usb.agent: Setup keyspan for USB product 6cd/119/0

• Belkin F5U109

Sep 12 14:59:34 localhost kernel: hub.c: USB new device connect on bus1/1, assigned device number 7
Sep 12 14:59:34 localhost kernel: hub.c: USB hub found
Sep 12 14:59:34 localhost kernel: hub.c: 2 ports detected
Sep 12 14:59:35 localhost kernel: hub.c: USB new device connect on bus1/1/2, assigned device number 8
Sep 12 14:59:35 localhost kernel: usb.c: USB device 8 (vend/prod 0x50d/0x109) is not claimed by any active driver.
Sep 12 14:59:37 localhost /etc/hotplug/usb.agent: Setup usbcore for USB product 451/2036/101
Sep 12 14:59:37 localhost /etc/hotplug/usb.agent: Setup usbcore for USB product 451/2036/101
Sep 12 14:59:38 localhost /etc/hotplug/usb.agent: Setup mct_u232 for USB product 50d/109/102
Sep 12 14:59:38 localhost kernel: usbserial.c: USB Serial support registered for Magic Control Technology USB-RS232
Sep 12 14:59:38 localhost kernel: usbserial.c: Magic Control Technology USB-RS232 converter detected
Sep 12 14:59:38 localhost kernel: usbserial.c: Magic Control Technology USB-RS232 converter now attached to ttyUSB0 (or usb/tts/0 for devfs)
Sep 12 14:59:38 localhost kernel: usbserial.c: USB Serial support registered for MCT/Sitecom USB-RS232
Sep 12 14:59:38 localhost kernel: usbserial.c: USB Serial support registered for MCT/D-Link DU-H3SP USB BAY
Sep 12 14:59:38 localhost kernel: mct_u232.c: v1.1:Magic Control Technology USB-RS232 converter driver

• Prolific PL2302 (single port)

Sep 12 15:01:38 localhost kernel: usbserial.c: Magic Control Technology USB-RS232 converter now disconnected from ttyUSB0
Sep 12 15:01:46 localhost kernel: hub.c: USB new device connect on bus1/1/2, assigned device number 9
Sep 12 15:01:46 localhost kernel: usb.c: USB device 9 (vend/prod 0x67b/0x2303) is not claimed by any active driver.
Sep 12 15:01:50 localhost /etc/hotplug/usb.agent: Setup pl2303 for USB product 67b/2303/202
Sep 12 15:01:50 localhost kernel: usbserial.c: USB Serial support registered for PL-2303
Sep 12 15:01:50 localhost kernel: usbserial.c: PL-2303 converter detected
Sep 12 15:01:50 localhost kernel: usbserial.c: PL-2303 converter now attached to ttyUSB0 (or usb/tts/0 for devfs)
Sep 12 15:01:50 localhost kernel: pl2303.c: Prolific PL2303 USB to serial adaptor driver v0.9