There are variations of the bowline that are more secure than the "standard" bowline described so far. Ones that I use include:
The double bowline (you can even start with three loops).
Rock Climbing Knots: Double Bowline
An even more secure bowline is the water bowline (recommending the second technique described by Sailaway21).
And many more, most of which I don't know other than the bowline on a bight.
And finally, a question. Another variation of the standard bowline I've seen tied results with the bitter end exiting to the side of the loop that is formed, rather than inside that loop (the rabbit runs around the tree the other direction). I think I recall being told that the purpose was to keep the bitter end out of the way when putting the loop over a cleat for example. Can anybody validate this purpose or know of another purpose?