The Mapping and Scripting tools are pretty mandatory for making a good hack, but there are bazillions of other tools with myriad other functions that are useful to you.
Karatekid's tool, the Gen 3 Hacking Suite, will do almost any editing involving Pokemon that you would ever need (stats, sprites, movesets, pokedex entries, evolutions etc.)
When I get stuck with the more complex programs, I usually fall back on Darthatron's programs (like Attack Editor Pro). They're simple, which is why I use it when other more complex programs glitch up.
What is this idea you said you had? If i knew what it was I might be able to recommend programs more suited to it.