A commonly asked question - I see it on SO, fb groups, quora and everywhere else. Few suggests python scripts, few suggests manual methods - here I am gonna share a very easy and quick method to view EC2 instances (or any other service) across all your regions without any scripting or anything.

Login to aws console and click on "Resource Groups" from the top bar, from the dropdown shown, select "Tag Editor".

From the regions dropdown, select "All regions", then select the resource type (AWS::EC2::Instance for this example), click 'Search resources'.