I've used Earth Balance vegan margarine on corn on the cob before without issue.
Beyond that, you honestly don't even need butter if the corn is sufficiently fresh... I've eaten sweet corn off the cob uncooked and with no other additions before.
If you're grilling it, I'd grill it in a good coconut oil. Boiling it obviously poses no problems, though you might be able to enhance the creaminess by adding a dash of a plant-based milk (the vegan twist on milk boiled corn).
But as for toppings not based in vegan butter at all, if you need to spice up the flavor of out of season corn, I'd suggest rubbing it lightly with a vegan mayo and then adding a shake of salt, a sprinkle of GoVeggie 'parmesan cheese' (or your preferred vegan parmesan substitute, or even just nutritional yeast would work, I think) and some chili powder.
P.S. You might get a bit more bang for your buck by posting this question to the cooking Stack Exchange, which gets vegetarian recipe questions a lot.