Crimson is right on the money. If your experience is limited, I recommend going on craiglist and buying a cheap bike, as you are going to lay it down. You can find lots of old bikes from the late 80s that still run like champs. Great for learning, cheap up front, and as long as you don't hurt it too much, you can sell it for a fair amount when you're ready to graduate to something better. If you want something a bit newer, a Honda Rebel 250 is a good place to start, or a Honda Nighthawk. A Ninja 250/500 would also be good. A Suzuki GS500 or Buell Blast would also be good starts. All can be had for under $1500 if you're willing to get something a little bit older (2004 and older, not at all bad).
I really recommend you go to a local dealership and just sit on the bikes and see which ones you fit on. You want to be able to firmly plant both feet on the ground while holding it up. Also, see how far you can safely lean it. Try not to get a heavy bike, and you will likely have to pick it up by yourself in the middle of an intersection at some point.