I will talk only about WxPython because it's the only toolkit I have experience with. TkInter is nice to write small programs (then it doesn't require a GUI Designer), but is not really appropriate for large application development.
- wxFormBuilder is really good. But it generates only .XRC files you need to load in your program. And this becomes a little tricky.
- DialogBlocks and wxDesigner are two commercial software which can generate Python code directly. I didn't tested these much because of their price.
- wxGlade is I think not yet mature enough for large programs, but it's worth a try.
After trying all these, I realized they had all flaws and that nothing is better than just writing the GUI in an editor. The problem is the extended learning curve. But then you will be much more faster and your code will be much more flexible than when using a GUI designer.
Have a look at this list of major applications written with wxpython. You will probably see that none of these use a GUI Designer, there must be a reason for this.
You then understand gs is right when saying that either you switch to PyQt or you write your application by hand. I had a look at Qt Designer in the past and thought this was what I needed. Unfortunately I PyQt has some license restrictions.