Aw man, TI Voyage - the greatest calculator ever made, to start off the flamewar...
Seriously though, I still use mine almost every day...even without dedicated exponent button. Especially the built-in Basic interpreter combined with full QWERTY keyboard will allow you to automate menial tasks really quickly, like calculating voltage dividers and spitting out valid E-Series resistor values...
Some guys even wrote a great little GCC extension that supports TIs kernel calls so you can use their CAS instructions like symbolic solving from your own little high-performance(compared to Basic) programs - awesome.
Mate of mine built a portable radio telescope from a satellite dish and one of these for data acquisition back in 2004, before the age of smartphones - awesome.