I would look at catalog_product_get_final_price , and a usage example at Mage_CatalogRule_Model_Observer::processFrontFinalPrice() . Please note that after this event prices are processed based on options; see Mage_Catalog_Model_Product_Type_Price::getFinalPrice() and Mage_Catalog_Model_Product_Type_Configurable_Price::getFinalPrice() .
Please keep in mind that setting up this feature requires a lot of testing with different quotation states, customer states, product types, etc. For example, consider a product that was first added to the cart, then updating its quantity from the cart. It is often necessary to implement logic in several methods / observers to handle all permutations.
Full list of events released in CE1.7 when a client is not logged in, new cart, simple product:
controller_front_init_routers
Mage_Cms_Controller_Router::initControllerRouters()
controller_action_predispatch
Mage_Log_Model_Visitor::initByRequest()Mage_PageCache_Model_Observer::processPreDispatch()Mage_Persistent_Model_Observer::emulateQuote()Mage_Persistent_Model_Observer_Session::renewCookie()Mage_Persistent_Model_Observer::checkExpirePersistentQuote()Mage_Persistent_Model_Observer::emulateCustomer()
catalog_product_load_after
Mage_CatalogInventory_Model_Observer::addInventoryData()
custom_quote_process
Mage_Persistent_Model_Observer::setLoadPersistentQuote()
sales_quote_config_get_product_attributes
Mage_SalesRule_Model_Observer::addProductAttributes()
prepare_catalog_product_collection_prices
Mage_CatalogRule_Model_Observer::prepareCatalogProductCollectionPrices()
sales_quote_item_collection_products_after_load
Mage_CatalogInventory_Model_Observer::addInventoryDataToCollection()
sales_quote_item_qty_set_after
Mage_CatalogInventory_Model_Observer::checkQuoteItemQty()
sales_quote_collect_totals_before
Mage_Tax_Model_Observer::quoteCollectTotalsBefore()
sales_quote_address_collect_totals_before
Mage_Sales_Model_Observer::changeQuoteCustomerGroupId()
sales_quote_address_collect_totals_after
Mage_Sales_Model_Observer::restoreQuoteCustomerGroupId()
sales_quote_address_collect_totals_before
Mage_Sales_Model_Observer::changeQuoteCustomerGroupId()
catalog_product_get_final_price
Mage_CatalogRule_Model_Observer::processFrontFinalPrice()
sales_quote_address_collect_totals_after
Mage_Sales_Model_Observer::restoreQuoteCustomerGroupId()
sales_quote_collect_totals_after
Mage_Sales_Model_Observer::setQuoteCanApplyMsrp()
sales_quote_save_before
Mage_Persistent_Model_Observer::setQuotePersistentData()
sales_quote_save_after
Mage_Checkout_Model_Observer::salesQuoteSaveAfter()Mage_Log_Model_Visitor::bindQuoteCreate()
sales_quote_item_save_before
Mage_Reports_Model_Event_Observer::checkoutCartAddProduct()
checkout_cart_add_product_complete
Mage_Wishlist_Model_Observer::processAddToCart()
controller_action_postdispatch
Mage_Log_Model_Visitor::saveByRequest()
controller_front_send_response_after
Mage_Persistent_Model_Observer_Session::synchronizePersistentInfo()