For App Store, search your application in itunes.apple.com and copy-paste View in iTunes link.
For Android, search for your application in Android Pit and copy-paste Android Market Link. Android Pit also provides QR code (2D barcode) for your application.
Note that URL shorteners (bit.ly) do not like market:// protocol, so you might need to use alternative http://market.android.com notation. This, however, prompts a dialog in the device “Would you like to open this URL in a browser or in Market Place?”