The HP 35s is one of the greatest calculators of all time. Ok, I’ll revise that statement slightly: it’s the best calculator I’ve ever used. The RPN system is incredibly intuitive and useful, besides being much more effective and efficient than the traditional algebraic system. The buttons feel great under your fingers, both texture and response. It has basically every function I’ve ever needed (in engineering undergrad), and despite having a two-line display, its far preferable to my TI 83, because it’s much smaller than the TI, and of sturdier build. I went to the 35s, never looking back.
[I wouldn't say Reverse Polish notation (RPN) is intuitive, but its easy to get the hang of. -- Mark]