Qt Designer is a GPL'ed GUI design editor provided by Trolltech as part of Qt. It generates an XML description of a GUI design. Qt includes uic which generates C++ code from that XML.
PyQt includes pyuic which generates Python code from the same XML. The Python code is self contained and can be executed immediately.
eric is a graphical debugger, written using PyQt, for debugging PyQt programs (or any Python program that doesn't use another GUI toolkit). Using eric you can single step through programs, set breakpoints (even while the program is running), and inspect and modify Python variables (again, while the program is running).
Note that eric is currently unsupported. If you would like to take over its development then let me know.