Talk with them. Not all snobs intentionally engage in such behavior; explaining to them that they do can sometimes get them to rethink their views and actions. Or, if they're purposefully being a snob, question some of their more egregious comments in an attempt to understand the snob's point of view. Counter with your own viewpoint to create an ongoing dialogue.
Ignore them. Snobs can make really asinine comments sometimes, but you can simply choose not to respond if they are infrequent. Dismiss the snobby comment by meeting it with silence, a disapproving sigh or a roll of the eyes. You can also walk away, thereby reducing the words' power or impact.
Confront the snob during a conversation by changing the subject and announcing how much you dislike snobbery and why. Speak clearly, calmly and articulately about how ugly and obnoxious snobbery can be, and how those who engage in such behavior tend to be insecure. This approach may cause snobs some embarrassment and could cause a few uncomfortable moments, particularly if others are also involved in the conversation or are listening in.