Toliken's "Not all who wander are lost," is good, but it's so overused no one can tell what you mean by quoting it.
When you quote something like "Don't look beyond the garden, Mrs. Savage. There may be a better place somewhere--but if you give this up to search for it--you may not find it--and lose what you have." (The Curious Savage, John Patrick) people are not distracted by the big names of the author, or in what context they have seen the quote before, or even the annoying fanboy who never shuts up about it.
So I ask you, what's you've favorite non-overused quote(s)?