Sick to death of nachos? So am I. There's no avoiding them anymore. I hear they're even cropping up at bridge parties. Ugh! And as for those corn chips: Well, the less said the better. But before you give up on nachos entirely, you should know this: There's a new one on the block. Well, not entirely new. Rancho Tejas (4747 San Felipe, 840-0440) has been featuring Gulf blue crab nachos ($7.45) for three years now. When I say new, I mean new to me. (I really should get out more.) But what a happy discovery they proved to be: lump crabmeat, three cheeses (Cheddar, Monterey jack and baby Chihuahua) and, best of all, not a Dorito in sight. Instead, Rancho Tejas substitutes corn and flour tortillas that are deep-fried. Believe me, polish off a plate of these things, and you'll beg for more.