Since you asked about scientific calculators, not graphing calculators, I've got to go with the TI-30x Multiview. Texas Instruments updates its TI-30 series every few years, and this was a really awesome update. On this calculator, fractions look like fractions, exponents look like exponents, etc. It's the first non-graphing calculator from TI that could do this. It'll also simplify square roots and give you exact values for trig questions (involving radicals, not just decimal answers).