There are a few wonderful websites online that show the history of calculators. I am very partial to Casio myself, but the Data Math Museum of Calculators has some very interesting history related to the TI series. Also, for those of you who grew up in the United States, one might remember the Little Professor calculator. This was often used by children for their first calculator. I had one as a kid and they are quite the collectors item today.
Another site, which is less TI focused, is Mr. Martin’s Calculator Museum website. Bonus in this site are links to particular slide rule and abacus related material.