PS: I know those aren't veggies, but I figured I'd list them in case you are feeling adventurous.

Arancini (risotto balls) rolled in breadcrumbs and fried, served with aioli? Mini meatballs and maranara sauce? Fried polenta fingers and bolognaise. Mini crabcakes with aioli.

Beet cubes would work great too, as long as you can provide skewers or toothpicks to prevent fingers fom staining. (And I am thinking goat cheese, or blue cheese dip)

Dip-able veggies to me is always the obvious carrot and celery. But to add interest is peapods or snowpeas. I like halved radishes and some cukes cut in sticks. I personally like cauliflower and broccoli florets, esp if the dip is right for them, like a feta, kalamata type dip. I do not find that many people really eat the multicolor bell pepper strips, although they look pretty in an arrangement. In general, as long as you have an assortment, it will look good, and everyone can go for the veggies that they like.

Watermelon radish (if you can find them), peeled and cut into wedges for dipping.

I like serve: blanched young carrots (keep the stems on + slice in half lengthwise), cherry tomatoes & fennel cut into strips lengthwise. For a "dip" I usually season a small bowl of my best olive oil with salt & pepper. Its rustic, very different and usually a hit.

I'm always a fan of pepper strips, especially red, yellow, and orange. I like to balance these with green vegetables like sugar snap peas and raw broccoli. (Of course http://food52.com/blog/6007-how-to-floret-broccoli-and-cauliflower-the-un-messy-way )