Foursquare — Best City Guide

Check in at Foursquare using this app and see where all your friend are.

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Gowalla

Use Gowalla to earn some nice prices while checking in

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Maps

Use Google Latitude to display your location on a map. Friends can see where you are and give you a call

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Google Buzz widget

use Google Buzz to buzz something and include a location

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Facebook

Facebook places it not available everywhere yet but it is a solid implementation of a location service. Use it from within your app

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