According to most folks out there, 1200 seems to be the "line thou shalt not cross" *cue spooky music*
LOL Seriously, 1200 should be your minimum, but there's no set magic number. Some people will go lower but you really have to make sure you get all your nutrients and stuff which can be hard when you eat very few calories (should definitely have a professional follow you if you decide to go this route for an extended period of time.)
I'm 5'6 and seem to hover around 1400-1500. But it really depends on the days. I eat stuff I consider "healthy, nutritious bla bla bla" and then check to see how many calories I consume, just in case I need to refer to it later if my weight gets stuck. There are days when my calories are lower because I ate lots of veggies etc. and the calories take forever to add up, and other days when I'm around 1800. I tend to focus more on the quality of the food (whole grain, fiber, veggies, low sodium, low saturated fats) than just calories and it seems to be enough to lose weight so far
If you see you lose weight at a certain level, no sense going lower than you have to. Sometimes, going lower doesn't necessarly equate faster loss. It seems to vary a lot from person to person. It also depends on how much activity you participate in everyday (from regular daily stuff to actual exercise).
There's a bunch of calculators here
http://www.3fatchicks.com/diets/diet-calculators.php that might help you
I only recently started tracking food and activities. Found this great little site. They give you points and stuff to track everything. lol And since I don't like seeing blank spots in my calendar, it's an extra incentive to track my stuff everyday.
Good luck!