Command-click anywhere in a Cocoa application's text area to open the URL at that point. Some Cocoa applications that come with Mac OS X include Stickies, TextEdit, Mail, Safari and Network Utility.
Control-click (or if you have a multi-button mouse, click with the right button) on a text area, and notice a "Services" menu at the bottom. This menu works the same as the Services menu in the menu bar. You can choose to remove unwanted services from this menu.