How to add custom menu item to sharepoint menu

Here is some link that demonstrate how we can add new menu item under existing sharepoint menu.

- To add menu item follow link shown below
(1) SharePoint 2010 Development with Visual Studio 2010: Add Resources (like Elements.xml) to Feature


(2) SharePoint 2010: Add custom menuitem to Welcome/My Settings (top-right) menu


(3) How to Add Menu Items to SharePoint with Features, Custom Actions, and Custom Action Groups

(4) Adding actions to Site Actions menu

(5) Adding a Custom Action to a Display Form for List Items

- Default custom action locations
below link lists different location and their custom action groups for different menu on different locations. 
(1) Default Custom Action Locations and IDs

(2) SharePoint: RegistrationId List Template Type IDs