Sin City redefines itself more often than Cher changes hairstyles. Las Vegas's latest incarnation- low-key sophistication- is revealed in its newest hotels. Modeled after an Argentinean estancia, the 201-room Green Valley Ranch Resort (2300 Paseo Verde; 866/782-9487 or 702/617-7744; doubles from $159) has a vineyard planted with Cabernet grapes. Vintage Vegas- think Desert Inn- is the look behind the 447-room Palms Casino Resort (4321 W. Flamingo Rd.; 866/942-7777 or 702/942-7777; doubles from $99). For the best views in town, visit the terrace of the 55th-floor Ghost Bar.