Another way to get the item's Id is to use dev tools like Firebug or hitting F12 on Chrome. Inspect the Network tab and find the ContentItemService.svc call, then switch to Preview tab. From there you can expand the Items collection and see the Id for each item that you want. Take a look at this video.
This approach is valid for each type of content items e.g. News, Events, Blogs etc.
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