I was wondering when someone was going to mention the CHI! It is the ABSOLUTE top flat iron. Even better than the ones that are more expensive. However, it is about $100, but, I have to say, I bought it about 5 years ago and it's still in perfect condition, use it at least 2-3 times a week.
Now, if you really dont want to spend that kind of money, a HotTools one is pretty good. You wont get that super sleekness that you would from a CHI, but then again, like the PP said, with flat irons, you really do get what you pay for (for the most part)!!
If you DO opt to get a CHI, DO NOT let the salesperson talk you into getting the Turbo. They will say that its better, bc you can adjust the heat, but honestly (I used to work at ULTA) there is NO need....You will always just keep it on high. Its just a waste of an extra 30 bucks.