greek yoghurt mixed with finely chopped cucumber, minced garlic or garlic granules, dried or fresh mint, and parsley if you like, and a pinch of salt also if you like. goes great with the meat being greek myself and will also taste good with the rice and veg.
this is what we eat in cyprus-tzatziki, always better made fresh but the bought ones are nice too and you can always spruce it up with any of the above ingredients and a dash of lemon juice.
you could also try tahini, which is different from hummous, and is made with crushed sesame seeds rather than chick peas as hummous is. Hummous in greece/cyprus isnt actually eaten with kebabs lol, it is used as a starter or side plate and only eaten with pitta or bread, and olive oil and lemon juice added to it.