One of my DM is running a d20 modern game and we are using gestalt for character creation. And it yielded interesting results. By using d20 modern character class on one side and a d20 class for another, it seems to be the key to the main complaints for FX spellcaster lagging too many spell levels behind. More interestingly, it allowed combination with classes not seen for traditional d20. My favourite so far for this style is the mix between d20 future and Eberro classes.
Look for this space as I would share the various builds I have come up with.