What would be a good side dish to spaghetti if you aren't making a salad?

wow everyone just copied the first persons answer. So I will give the special answer of cheesy bread.

Everything goes great with cheese

Agreed. Garlic bread is the best alternative, but breadsticks would be yummy too.

Garlic Bread      

garlic or herb bread or some french fries or even some mashed potato .

Garlic bread / doughballs.

You could make a 'Pan Gritatta' made with fried breadcrumbs, olive oil, herbs, parmesan mixed and sprinkled over the pasta. 

Just toasted garlic bread

Homemade Garlic bread. 

Minestrone soup or broccoli rabe come to mind.

Mashed potatoes?   

You could cook and cool broccoli or asparagus, chop and add diced onion, red bell peppers and dress with balsamic. 

Crust bead would be a compatible side too.