If a program can be written in Tkinter, this is probably the best way to go in terms of simplicity and maintainability. However, in case the aforementioned limitations get in your way, you can explore some other alternatives to Tkinter.
In addition to Tkinter, there are several other popular Python GUI toolkits. The most popular ones include wxPython, PyQt, PySide, and PyGTK. Here's a brief discussion of these toolkits.