Do you ever find that a rectangular window just won't do? Try keying in CP (Crossing Polygon) or WP (Window Polygon) at the select objects: prompt. You will be able to create your own polygonal window with as many vertices as you want - CP will select all objects within or crossing the window, WP will select only those objects within the window. Only one rule here - the polygon cannot cross itself!
Note: CP works great in the Stretch command...