Well, your kit lens covers the 35mm portion. So I personally wouldn't go there, just yet.
I just picked up a Tamron 70-300mm lens for about the same price as the 70-200. I love it, and it recieved some rewards too. Very nice lens. And since you're returning your 70-300. I notcie you don't have anything wider than the 18mm on the kit lens. Have you considered a fisheye or wide angle like the 10-22mm range? Or maybe a macro lens?
Also, if you are into being a bit more artistic with your photos, go with a lens baby (tilt shift), I love mine.
Also on the artistic side, have you ever considered IR photography? Its really fun and a good set of IR filters will cost you$50-100.
I'd look at a good tripod. I have one of those cheaper Walmart quality ones, and I can tell you a tripod is in my near future, very near future.
How much do you use your flash? Enough to warrant upgrading your flash? Or maybe adding a ring flash to your kit?