A (not-so) simple little javascript loan calculator I wrote for extra credit in two classes (javascript and finance) at PSU (hence the PSU color scheme).
Enter values for whatever knowns you have, and it will calculate the rest once you have entered enough data, if it is attempting to calculate values for something that you don't want it to, click the lock icon to prevent the value from changing
Click the "show amortization table" check box to see the full amortization table for the current loan.