Tucked away in the shell of an old K-Mart in a west Houston strip center that defines the word "unassuming" is one of the city's best markets and -- dare we say it? -- the best salad bar around. There. The secret is out. Sandy's Market doesn't look like much as you pass it on Katy Freeway, almost lost in the shuffle of endless beige stucco buildings that line the city's roadways. But step inside......