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I picked up an HP-30b a few days ago from ebay for less than $20 and absolutely love it so far.
Don't let the designation "business professional" put you off. Yes, it has some weird stuff like Black-Scholes stock pricing menu, but the rest is pretty impressive.
Of non-"business professional" stuff it has:
10 named registers (0..9)
100 indexed by reg0 registers (shared with cash flow and statistics)
trigs
hyperbolics
IP,FP,exp,ln,gamma,c(m,n),p(m,n)
cdf and inverse distributions (normal,chi2,F,t)
random numbers with assignable seed
linear,power,exp,log,quadratic regressions
RPN (optional, if you are RPNophobe)
KEYSTROKE PROGRAMMABLE with 10 programs, each can be assigned to a hotkey. That is, if you do not use IRR button (or don not know what it does), just assign your favorite program to it and call it with a single keystroke. conditional jumps, loops, subroutine calls (4 level call stack)

The business part is not so useless too. Date arithmetic is useful in its own right. Percentage calculation is of general interest. So is True Value of Money -- everybody has to deal with loans nowadays.

In my opinion, it is "calculator done right", finally. The only thing I think is a mistake on their part is shifted STO key.