Nobody has mentioned this, but have you tried using Spotlight? It has a built-in calculator and evaluates as you type. Here's what I know:
* It uses infix notation; * allows either `a ^ n` or `a ** n` syntax for exponentiation, but not pow(a, n) * sqrt(a) * exp(n) * pi and e, possibly other constants * trigonometric and cyclometric functions, but no reciprocals The only drawbacks I've seen so far are that it's not a fully-fledged programming language like bc and it doesn't support radices other than 10. If I need more advanced features, I usually fire up a Terminal window with irb.
