If you're super anal about accuracy, get one of the lab-grade one that goes to 1.070. Just know that if you brew any bigger beers, it will be worthless. If you want to get something that's fairly accurate and will cover most of your brewing needs without breaking the bank, then the 5 dollar beer/wine hydrometer is fine to start with.
Like many brewers, once you get into the hobby you'll probably end up buying a refractometer for doing your pre-fermentation measurements anyway.