Things I do to a punchy sound on my rhythm- tck-ch articulation on the blow, lip pops, and switching quickly between draw and blow on the same hole(s). There is a trick you can do where reversing the airflow kind of cuts short the previous note, or even just closing your mouth after hitting the note will make it a little more staccato. The tck-ch is my main tool though. I do it loudly enough so it's audible, kind of like a little beat boxing but it blends in. Too much reverb/echo can muddy it a bit. Don't lag the beat.
As for crazy things I've done with harmonicas- I took the covers off of a harp once and took a toothpick and put it on the reed. Basically I used it like a finger on a fretboard to bend notes. I got the feeling that if I devoted many hours to the study of the technique it might turn into something really interesting, but holding the toothpick like that cramped my hands and the missing cover meant my mustache hairs were fair game. :)
