Just finely shred up your chosen veggies - cabbage, carrot, spring onions... personally I love fruity coleslaw (almost a crossover kind of waldorf salad!) so I also add some fresh mandarin segments, handful of sultanas, chopped apple and some walnut halves. Then you can use Helman's extra light mayo to dress it, or mix the light mayo with some quark - add your chosen herbs and plenty of black pepper for flavour. Nenya's balsamic vinegar suggestion sounds fab, too.
You can also make a lovely curry coleslaw just by adding a spoon of garam masala. Personally I'm addicted to cumin so I add it to nearly everything! Lovely warming luscious spice. <3