IF you want to keep it simple, steamed carrots/broccoli/cabbage/cauliflower, corn etc are all nice and easy. A bit of butter and salt makes them a million times better.
Other options (beyond the great ideas already on this thread) :
A quick veggie stir fry with whatever veg you have that might work - n our case usually onion, carrot, tender stem broccoli and baby corn - flavoured with some lime juice and soy sauce.
Cauliflower and broccoli cheese
Roasted cauliflower seasoned with your preferred spices.
Chargrilled greens - leeks, cabbage, cavalo nero, spring onions or whateverver you have etc. Can be served plain but I like to make a dressing by adding some garlic, lemon and honey to the pan just before they're done.
Similarly, mange tout are great just fried in a dry pan for a few minutes with a bit of olive oil after. Goes especially well with things like fish I find.
Honey and cumin roasted carrots.
Mashed butternut/sweet potato.
Asparagus with lemon butter
Fried mushrooms.
Lightly dressed rocket - under rated as a nice accompaniment to a lot of meals.