You have no idea how much you will use a mandoline until you have one. Carrots are suddenly standing at attention in a perfect julienne, potatoes are sliced so thin you can make anything from home-fried chips to pommes anna, bell peppers come flying out in such whimsical cross-section squiggles that you'll want to wear them as bracelets.
Our favorite mandoline is not the big stainless professional-grade one we used in cooking school. No. It's the Benriner: a budget version you can get in Chinatown at Kam Man food Products, 200 Canal Street (Mott Street) or Pearl River Mart, 477 Broadway (Grand Street). Ours was $22 a few years ago. They seem to be in the $25-$35 range these days.
One word of advice: don't be a show-off. Watch your fingers. No one wants a fingertip in their salad.