Stickers are a good one, because as well as a neat little gift and promotion towards the people that you give them to some of them will end up stuck on school/college folders, guitars, laptops and all sorts of bits and bobs which other people will see, plus if you're doing a gag strip and can pull off a good one panel strip then that's perfect.
The other thing that could be interesting is something like the Cubees that are on the Sister Claire site
here. Depending on how much it would cost to have them printed up then they could be an interesting alternative to normal flyers, still containing some information about the comic on the other side as well instructions, but of course that largely depends on the size and complexity of the model.