Spagetti, Alfredo and Vodka Sauce
I find that spinach and broccoli work best with sauces. Personally, I like broccoli the best since it doesn't have as much water as spinach, which can water down the sauce.
Meatier vegetables like sweet peppers, asparagus, and mushrooms work well as lasagna noodles. Asparagus is more expensive unless bought in season during the summer, but because it is my favorite vegetable, I will occasionally indulge in the fall and winter. Sweet peppers can also be expensive unless bought in season or during a sale. Mushrooms are probably the cheapest depending on the type of mushroom and the size of the pan.
I got this idea from a paleo-diet blog awhile back, and it's a great idea. If you like having the noodles, consider julienning some vegetables to mimic a noodle. Carrots julienne pretty well along with many squashes (both winter and summer).
I've tried all of these options and to be honest, I actually prefer them to noodles. Along with being healthier, I feel satisfied and energized when I eat the vegetable alternatives. I definitely won't stop eating noodles, but now I just eat them for a special occasion instead of daily.