For a perfectly square table you may be tempted to use four matching pieces for a perfectly symmetrical look. However you can get a more intriguing look by using two pieces or groups one in each corner. Try a tall vase or lantern in one corner with a stack of two or three books in the other (and an airy sculptural accent on top).
Old pallets or crates are a fine alternative to the traditional coffee table and are incredibly versatile too. The ones here have simply been turned upside down — but you could screw yours together if you tend to move your furniture around a lot. You could also stack them or cut them down to size or use one pallet and elevate it with small apple crates for example. A coat of paint will transform the trusty courier once again.