Students in General Math, Algebra I, Geometry, and Consumer/Business Math are not required to have a calculator, but it is recommended. I have a set of calculators that students can borrow during class, but I don't allow them out of my classroom.
If you don't already have a calculator and plan on buying one, I would recommend the TI-30X IIS, which is the same model as my classroom set. It includes trig functions (which we use in Geometry), and it is the calculator with which I am the most familiar. You can find information on where to buy the calculator by clicking here.
If you already have a different calculator, that's ok - we can work with a number of different models.