USB Drive Letter Manager (USBDLM) is a Windows service that gives control over Window's drive letter assignment for USB drives.

Running as a service makes it independent of the logged-on user's privileges, so there is no need to give the users the privilege to change drive letters.

It automatically solves conflicts between USB drives and network or subset drives of the currently logged-on user.
Furthermore, you can define new default letters for USB drives and much more.

USB Drive Letter Manager (USBDLM) can:

check if the letter is used by a network share of the currently logged on user and assign the next letter that is available
reserve letters, so they are not used for local drives
assign a letter from a list of new default letters, also dependent on many different criteria as the active user, drive type, connection (USB, FireWire), USB port, volume label, size, and others
assign letters for a specific USB drive by putting an INI file on the drive
remove the drive letters of card readers until you insert a card
show a balloon tip with the assigned drive letter(s)
define autorun events depending on many different criteria
many other things, see help file, available online as HTML version too

Similar:
How to Optimize USB Drives for Better Performance
How to Show or Hide the Safely Remove Hardware Icon
What Is an SS USB Port?
How to Diagnose USB Problems

  Download