For College Algebra, Trigonometry, Precalculus Algebra & Trigonometry, Geometry for Education, Calculus I and Calculus II: A scientific calculator.
A cheap ($9-$20) scientific calculator is all you need. If you are not sure how to tell if a calculator is scientific, it must have a key labeled SIN to be scientific. The only scientific calculators that you may not use are the Casio FX-82ES, FX-83ES, FX 85ES, Casio FX-115 (ES, MS, ES Plus or MS Plus), Casio FX-300 (ES, MS, ES Plus or MS Plus),  Casio FX-350 (ES, MS, ES Plus or MS Plus), Casio FX-570ES, any Sharp Write View calculator, the HP SmartCalc 300s, the TI-36X Pro and the TI-30XS MultiView calculator. Graphing calculators and programmable calculators are not permitted. If you have to purchase a calculator, I recommend the TI-30XA.

For Social Choice Math and Finite Math: A calculator with a square root button.
   Graphing calculators are prohibited.  Scientific calculators are permitted, but not required.

For Differential Equations: No calculators permitted. (Sorry, it is a departmental policy.)