Most unsecured creditors will be listed on Schedule F, such as credit card debts, medical bills, etc. Schedule E creditors are those unsecured creditors which have priority over general unsecured creditors. The most common of these are domestic support obligations and tax debts, as well as other special ("priority") debts.
Non-priority claims listed on Schedule F are dischargeable. Priority claims listed on Schedule E are either non-dischargeable or are entitled to payment above other creditors if there are assets available.
If you look at the first page of Schedule E there are a number of different types of debts that are considered unsecured but priority. This includes domestic support obligations, wages, salaries & commissions, etc. The most common type of unsecured but priority debt are taxes and certain other debts owed to governmental units. Each type of debt listed on schedule E provides for specific code sections to review discussing further those types of debts.