My father had a HP-45 from work, which had the secret stopwatch mode.
The HP-35S is the only current HP worth buying; eventually I'll get one.
My current main calculators are a HP48G+ (which I bought used since I wanted a 4 line stack display) and a TI-89 -- both are very nice, and I still enjoy using them.
I still have a HP-41C with quad memory and some cool books (including HP-41 assembly language programming). The HP-41C needs its zero key fixed; hopefully I'll get around to that sometime this year. Once it's fixed, I haven't decided what I'll do with it.
My first calculator was a HP-34C; I learned to program on it.
@Antedeluvian, why don't you replace your NiCds in your 35,
I did, twice. But it was expensive. My career progressed to the point where I needed a programmer's calculator for all the binary<->hex<->numerical conversions and I ended up with a Casio for much less than the price of NiCds. The Casios have come and gone though- the HP35 still has a place of pride on my shelf. I now use the HP35s which does meet all my requirmements.
@Sven, in answer to your question, "Are you interested in my recollections...? my answer is a very definite YES. However there will be others who will find your FPGA musings of greater interest. So why not do both and keep everyone happy?