With Marth, I perform random dashdances, wavedances, double fairs, SH fair -> waveland...pretty much any tricky movement things Marth has.
With Falco, I'll stand in the middle of the stage and alternate SHL (one left, one right) with shines in between each one, usualy. Sometimes I like waveshining around too, or empty pillar. If I'm on Brinstar (not the one with Kraid. The one with the rising and falling lava), I'll break those weird gooey things holding the platforms down by pillaring them. If I KO my foe up, I have enough time to run over to the other one and break it too. Thats always fun.
Oh, and when I play Jiggs, if I KO my foe up, I'll hit rest on purpose. I wake up RIGHT before he respawns. One time a Fox tried to get a quick JC usmash on me after I did this, but I shieldgrabbed him at the last second (well acualy, it couldn't have been the LAST second, otherwise I would've powershielded
), then proceeded to uthrow -> rest him for another KO.
EDIT: omg, I forgot the best taunt! As Pichu, after a KO, I'll use Thunder a few times (damaging myself) and say to my opponent "You seem to be having some trouble. Here, let me help you out a little" XD