How can I input values to my arduino without needing the serial monitor? Would I need to write a separate GUI to make that happen?
Use Hyperterminal if you have XP
Realterm is a really nice free one if you don’t have hyperterminal.
realterm, teraterm - free serial consoles.
If you want something that simplifies things by using buttons and textboxes you will have to write your own.
Then things like ease of development, portability and deployment come into play.
Tcl/tk has super easy serial support, runs on darn near anything processor wise,and packs into a neat, small single file executable.
C/C++ will work, gui toolkit is up to you.
Java if you only need to run on windows, single jars and serial support are ok.
perl, python, ruby, etc, most will use Tk for gui, but you can use others.
M$ Visual Basic etc, for windows only.
You should try using HyperSerialPort for communicating over serial ports. It is written especially for microcontroller code development. It has built in tools like the Send Characters Timer which repeats characters using a timer. Also, you can use the Embedded Scripting Evaluator which allows you to write Python scripts to perform conditional branching while using the serial port. http://www.hyperserialport.com