How Do I Delete My iPad & iPhone Back-ups?

[Moose]

I recently purchased a 64gb iPad 2. I plugged it into my MacBook and started syncing it, and when I looked at the space on the hard drive of my MacBook, the 18gb I had free were gone! I Googled how to delete back-ups for iPad (I also have an iPhone), and I deleted the extra ones, but it barely freed up any space. I cannot figure out where the extra space went, and it's really starting to bother me. Is there a way to prevent iTunes from making copies of my iPad and iPhone libraries, and to delete the back-ups without causing a problem for my devices?