What are you hoping to do with it, i.e. commute around town, take long interstate trips, put it on the track, etc.? Once you determine that, you can make a better decision on what to get. Look for something relatively small, as a lighter bike is far more forgiving in low speed maneuvers. Don't worry about power. Even the lowly Rebel 250 can cruise on the interstate if needed to. I've personally done 3+ hour trips on the highway with one and it never gave me a moment's trouble. Fantastic commuter bikes (as are the other small engine bikes like the GZ and TU250, EX250, Suzuki S40, etc).
If you want a cruiser with a bit more power, something like the Suzuki S50, Kawasaki Vulcan 500, Honda Shadow VLX 600, etc are great options.
On the sport side, you can get an extremely practical bike in the Yamaha FZ6, Kawasaki EX500 and EX650, and the Suzuki SV650. All are lightweight, cheaper to buy than their pure bred sports brethren, and much easier to ride long distances.
Consider your options and see what's available locally. Find something that's already been dinged up a bit on craigslist. You can find plenty of wonderful first bikes for less than $2000 that are easy to maintain and ride until you get several thousand miles under your belt and know exactly what you want long term.