The straight line selection

Using the pen tool, it is easy to select around a straight edged shape with simple clicks.

Click on a corner as a start/anchor point. Move to the next corner and click again and so on until you return to the beginning again (as shown below 1-2, 2-3, 3-4, 4-1). For straight lines, holding down the shift key as you click the path retain right angles.
Note that the 'paths' palette has its own tab in the layers/channels palette and you can see your progress as you click around the shape. Easy peasy!

Double click on the 'work path' layer in the paths palette and click OK when the 'save path' box appears. The path is given a name and saved as 'path 1'.

At any time whilst 'path 1' is highlighted in the paths palette, you can click on the selection button at the bottom of the palette (shown above) to convert the path into a selection that you can work with. Since the path is saved, you can go back to it at any time and load it.

You can have as many paths as you like in a document, just ensure that you are working on a new path layer each time you create one, so that it can be saved on it's own....