If you like Gin, London Gin club, just off Oxford Street. Tasting menus are great to share, and look very classy.
Nearby (Rathbone Place) is also Bourne and Hollingsworth, a prohibition era styled cocktail bar, doing things like alcoholic teas and very interesting cocktails.
Moving to Camden, I'm a fan of fifty five bar, especially during their happy hours. They make some awesome and unusual cocktails.
If you want more of a dinner date, I cannot recommend Brasserie Zidel near Picadilly Circus highly enough. Looks super classy, great food and awesome prices, especially the fixed price menu...
All of these have been excellent date fodder for me.