ONLINE CALCULATORS
Online Scientific Calculator
Complete with SIN, COS, and TAN keys.
Online TI-83 Graphing Calculator
This will only work if you are using a PC. If you are on a Mac, try the link below.
Online TI Calculator for Macs
I haven't tried this on a PC, but it worked for me on a Mac. You have to read the directions and download a rom image though.