Well, if you plan on taking physics or possibly engineering courses, I'd like to suggest the Hewlett-Packard HP49G+. The 49G+ offers expandable memory whereas none of the TI's do, including the Voyage 200 and 89. The 49G+ features a full computer algebra system, even more complete than the 89 and Voyage 200 in most cases. The 49G+ by default has more advanced math functions than the 89 does. You could download them for the 89 from a third-party site, but why bother when you can buy a calculator with them already on it. The 49G+'s price is very comparable to that of an 89, roughly $135-$150 (USD). The 49G+ offers RPN mode (faster data entry), and an algebraic entry (which, I don't prefer) that uses parenthesis. If you don't like RPN, then switch to Algebraic. Like I said, you can't go wrong.
However, if you don't plan on taking mathematics or physics classes that aren't "upper division," the HP is useless as will be the 89. In that case, go ahead and buy the 83+.