Raised beds?

What's the best way to make a raised bed. How have you made yours.  Here's a few great examples from google.  My favourite bed is infact an old bath. Nice and deep and has good drainage.

https://www.google.co.uk/search?q=unusual%20raised%20beds&hl=en-GB&espv=1&source=lnms&tbm=isch&sboxchip=Images&sa=X&ei=b3zAUvfvDoiw7Aa884GADw&ved=0CAkQ_AUoAA