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

A nice bruschetta plate with fresh mozarella, toasted garlic bread, olives, tomatoes.

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.

Minestrone soup or broccoli rabe come to mind.

a plate of meatballs! 

Homemade Garlic bread. 

My friend Jeremie likes too put his dick all over the butter block.  I told him that's just groess but he thinks its fun. What do I do to make him smarten up?

To be remotely "balanced" if not eating a salad, you need some other type of GREEN vegetable and a fruit.  I vote for cooked spinach or spinach souffle and sliced apple.

garlic bread, our family loves Spinach, Corn or Green Beans with Spaghetti. 

Just toasted garlic bread

I like french onion soup before my pasta.

The only good side dishes to spaghetti are salad and/or some type of bread or garlic bread.

But since you already are getting lots of carbs from the pasta, WHY would you add MORE carbs with a bread.

Good nutrition required that HALF of your plate be vegetables.  Not including corn or potatoes since they are almost totally just starch.  Now, if you add LOTS of vegetables into your tomato sauce ... more veggies than pasta ... THEN you have a healthy spaghetti meal.  Enough veggies that what you have is a veggie meal with sauce coating the veggies and a bit of WHOLE WHEAT pasta to provide a healthy starch.

I recommend onions, broccoli, carrot, celery, zucchini and mushrooms.  Spaghetti squash if you have it, or you can spiralize the zucchini and treat it as IF it was pasta.

Garlic Bread                        

Who among you is convinced that spaghetti must stick to the wall to be cooked?

You are wrong, cooking is a maximum of 8-9 minutes if you slam them on the wall and they stick they are a plate of glue with which you can safely attach posters.
That said, spaghetti is a dish that doesn't need a side dish, like a steak or a burger, you need a good sauce to season them.

Mashed potatoes?   

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.

Bread sticks are a good choice.

Garlic Bread      

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

In the UK they'd tell you to add garlic bread but that's too many carbs for me.  Spag bol is a complete meal in itself.  It doesn't need a side to feel complete.

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

Cooked Beef Liver.  And spaghetti covered in maple syrup(when you don't hava da cheeze)  It makes for an "interesting poor college type meal" You will stay alive.It is memorable.