spring vegetables are beautiful right now and pair wonderfully with pasta. Try green beans, broccoli, asparagus or create a salad out of whatever veggies you find at the farmer's market with a nice vinaigrette. It'll be a hit!

I think a fava bean crostini could be nice, you can make the puree part ahead of time. I don't have my recipe on hand, but this one I found seems very close:

http://www.foodandwine.com/recipes/fava-bean-crostini

Also: at a friend's recently she sauteed, in a combo of olive oil and butter, snap peas and radishes. Delicious and colorful! I had never thought to cook radishes before, I admit.

Ditto on veggies. You've got pasta and cake, so I wouldn't do something bready. And serve Prosecco or rose of course!

a salad with fresh vegetables would be a great addition to the meal. Or grilled or roasted vegetables. Try this roasted asparagus with orange slices.

Since you're doing a pasta entree, how about a big platter of antipasto? Cured meats, cheeses, olives, marinated vegetables (grill 'em if you want), sliced melon to eat with the prosciutto etc. Serve with bread. If you want to augment it further, you could have something like tapenade or perhaps a white bean dip. I went to a catered party the other evening where the salumi and cheese display included sugared pecans (which tasted amazing with the cheese).