Droid Calc

Finally a calculator which looks good and has what you need!
If you feel like simple calculations just use it in a portrait mode.
However if you turn the screen you will get scientific calculator including features like:

*Traditional algebra operations
*Braces
*Sin
*Cos
*Tan
*Ctg
*Ln
*Log
*1/x
*Factorial
*Percent
*Sqrt
*Abs
*E number
*Pi number
*x^2
*x^y

Have fun ;)