Price sets allow you to set up flexible multi-option pricing schemes for your contribution, event and membership pages.
Event
Contribution
Membership
Text/Numeric Value
Select
Radio
Checkbox
Add to a Contribution or Event Page
CiviDiscount
This extension allows the admin to create and manage discount codes that can be used on membership and event pages.
Group-Based Pricing
This allows you to implement things like members-only pricing for events. (by using a Smart Group to track current members) This extension works with both static and smart groups.