Most of the voltage divider calculators on the Internet make the assumption that the user needs to find out what the output is from a specified input and known pair of resistors; I've written a Java application that basically works backwards from that: the user enters the input, the desired output, and the application cycles through and figures out what combinations of fixed resistors will produce it. The application allows for 5%, 1%, and .1/.25/.5% resistors, can copy the values to the system clipboard or print them out. Included in the file is FULL source code (with libraries and everything else), and well as the Java .jar file (neatly stored in the dist subdirectory). It's available as a zip at:https://sites.google.com/site/adifferentlemming/Home/projects/arduino#TOC-Voltage-Divider-Calculator---New-an
It's released as Open Source, so feel free to molest and mangle it to your hearts content!