HP's range of RPN calculators are legendary. None more so than the HP 12c. It's remained largely unchanged for over 25 years and it is still the most amazing quality ever. You will not find a more tactile and robust pocket calculator anywhere.
If you've never used a Reverse Polish Notation machine before, you don't know what you're missing. Not only is this entry method super fast and efficient (it saves on keystrokes compared to the more common algebraic entry method of most other calculators) but it's also more logical, especially obvious when entering problems that are written with multiple parentheses. Another benefit is that the HP12c can calculate date problems in either the UK's DDMMYYYY format or the US's MMDDYYYY format. It understands leap years too without you needing to worry about them!
You probably already know that this beast is programmable too. It has many built in routines for common financial problems but also a memory for 99 key entries in your program. Also, for flexibility, you can make instant use of the 10 registers (instead of a normal calculator's single memory function).
After a little time learning the basics of RPN, you'll never want a standard calculator again.