I collect as well:

  HP-35 (1972, first scientific, first in space) - in leather case
  TI-30 (1976, first low-cost scientific)
  HP-12C (1981, financial, c. 2000 remanufacture)
  HP-15C (1982, advanced scientific) - in leather slipcase
  HP-16C (1982, computer programming) - in leather slipcase with manual
  TI-30 SLR (1982, TI’s first solar-powered scientific)
  HP-17B II (1990, financial)
  TI-85 (1992, TI’s first with link port)
  TI-82 (1993)
  TI-92 (1995, TI’s first with computer algebra system)

I use the HP-16C pretty regularly when I'm working on network protocol programming. I have good apps that do it, but there's something about having the calculator right in front of my keyboard rest and turning to it that I like more. In a pinch or outside the house I'll use JPRN instead.

https://github.com/zathras/jrpn