Have fun! Let us know if you come up with something cool!
One last thing, if you're not in edit mode you can drag and drop waveforms onto the live.drop (Maxforlive is not necessary). You can overlap the waveform~ object (which visually displays the waveform) with the live.drop to create a sorta visual version of live.drop.
Oops, here's an updated version with the presentation mode made to look more... presentable.
I am trying to build a series of tutorials that start with basic FM theory, then go into subtractive synthesis, more advanced FM, then finally a fully-fledged 4-operator FM synth, I'll post it in the forums when I finish it....
Other fun things to try:
Use a pictslider to create a 4-point waveform interpolator (just crossfade—wavetables have the advantage that morphing is LITERALLY just crossfading because the phases always line up)
Try a a tapin~ and tapout~ to create FM feedback. You can make some truly horrible growling.
Try PM instead of or in addition to FM, it can make some pretty good robotic sounds.
Use poly~ for upsampling, it will allow you to modulate further before things dissolve into noise (but sometimes that's what you want)
Construct your own single-cycle waveforms
Modulate the index with LFOs, ADSRs, or LFOs modulated by an envelope (to create LFOs whose speed changes over the course of the envelope)
It's way easier to use the signal as the modulator, since you're just multiplying it by some large value and using it as an offset on the carrier's frequency. (i.e. you don't really have to modulate it, just an oscillator, which is easy)
An alternative is to use an envelope follower on an audio signal and have that change the modulation index based on volume.
To piggyback on what Peter was mentioning, here is a PureData tutorial for creating an FM patch that uses a guitar signal. It is trivial to migrate over to Max (although you need to grab the Max version of sigmund~ here http://crca.ucsd.edu/~tapel/software.html). I did just post this in another thread but the part that makes it interesting is the amplitude of the guitar signal changes the index of the FM synth, a little like what Peter was describing with envelope following.
I posted the QM patch as an example of how you can tinker with the bog-standard FM algorithm. Admittedly it is something of a one-trick-pony, but should inspire you to experiment with routing, feedback and quantization options in your own synth.