You can easily plug into anyone's computer with your iPhone and his or her normal connector cord, but you have to make sure that you do not allow a sync to happen. If this happens, you can place all of your media on their computer or their iTunes contents will move its way onto your iPhone and delete your contents.
Make sure that you plug your iPhone into the computer and wait until there is a prompt asking if you want to format, that way you can make sure that you select no. Even once you do, you can let it charge without a problem. This is always going to be more reliable that an iPhone wall charger.