Edit: .....THERES A BASE BUTTON!? TI83 has too many buttons!!
Well mine just has buttons for binary, octal, decimal and hexadecimal, but it is about 13 years old. If a calculator was around which let you convert to arbitrary bases from 2..36, I'd be mildly impressed.
Here you go, for your delicatation and delight, a calculator that will convert between any base from 2 to 36
It's still pretty rough around the edges, but the calculation engine is working nicely. I had some fun this weekend programming it. It requires .NET Framework 2 to be installed, otherwise just unzip it and double-click to run.