Gab or Gabs being the most common. Although I should warn you if you are not a good friend of mine and you call me Gab or really even Gabs it kind of irritates me. (and if you have to ask yourself "am I a good enough friend to call her that" then you are not:) And for those who are not, I would like to point out that really the name Gaby is a nickname altogether... short for Gabrielle. So don't feel excluded, we are still friends.
I think my Favorite nickname of all time I owe to my dear friend Capree..... who coined the name early on in our time in the BYU photo program "Gabitron" It was just one of those things that has stuck and really become so much a part of me now that it doesn't really even feel like a nickname at all. It is scribbled on my notes books as "this book belongs to..." it is on all kinds of boxes of film and paper.. and has earned the honor or being laser scribed onto the back of my ipod.
But there are other acceptable nicknames too. Gabers (only my sister Catherine, However, can call me Gabers McDabbers, and not end up punched in the arm... so don't try it!) GiGi (preferably said with some little french accent) and Red.
As far as unacceptable nicknames go.. only the mildly bad one will be shared. One for example, I thought had died after I left college and was no longer around a certain friend of mine by the name of fletcher :) Graby, is and will never be something funny or cute to call me. Like I said I thought that this one had gone the way of the wind, but somehow it has lived again with the help of my friend Ty. Who I must also add is responsible for a great deal of the nicknames that won't be mentioned here;) But who so kindly reminded me last night of the halloween nickname gaba gaba doo! Not really a recommended name either.
Oh and while we are on the topic of my name. Jokes about me talking a lot 'cuz you know my name is gaby, were not even original when I was 9 so don't try:)