Hackers might delight more in the HP-16C "Computer Scientist" calculator[1]. It can be set to perform calculations on variable word sizes up to 64 bits, which is amazingly useful when you're working with processors that use non-standard word sizes (e.g., the 29x22 bit fixed-point ALU from a chip I worked on for a few years). It's also a great way to teach someone to program assembler, since it's programmable in a rudimentary RISC style.
Full disclosure: I'm something of an HP calculator nerd. I have an 11C, a 15C, a 16C, a 32SII, and a 42S. Once you get used to RPN, you will never want to go back to algebraic calculators.
I'm a 42s diehard, but the Free42 app for iPhone has gotten so good that I'm not using the real one anymore (and it's larger than the iPhone which is off-putting)
Still, another great calculator for programmers. The extra fn keys are great for working with large hex values.
Though of course the 16C is only available from eBay at blood-curling prices. I'd love one, but it's just too hard to justify a few hundred dollars to upgrade from a perfectly functional 11C.
Full disclosure: I'm something of an HP calculator nerd. I have an 11C, a 15C, a 16C, a 32SII, and a 42S. Once you get used to RPN, you will never want to go back to algebraic calculators.
[1] http://www.hpmuseum.org/hp16.htm