Steam Role is the ultimate admin utility. True to it's name, this application is a power tool for inspecting and modifying your Sharing Model including: Roles, Territories, Public Groups, Queues, and Users. You can even use it to mass-reassign records.

Appropriately named, Draggin' Role allows an administrator (or delegated administrator) to drag and drop users from one role to another, and to drag and drop roles around the hierarchy. Small but mighty, this app is especially well-liked because it's free!

Ever wish you could run reports on the standard and custom fields you have in salesforce? Take a Field Trip! This utility lets you analyze the fields of any object, including what percentage of the records (or a subset of your records) have that field populated.