STAFF PICK: Rainbow Guitars has a long-standing reputation as a full-service "players" store. With the move to their new digs a block north of the old store, a good thing just got better. Percussion, keyboards, sound systems, instruction, racks of new Stratocasters, Les Pauls, Martins and Ricks...the straps, strings, sticks, pedals, and other essential accouterments make Rainbow a picker's paradise. Need volume? You'll find everything from miniature Dan-O practice amps to Marshall stacks that'll blow your garage down. The vintage instrument room, the domain of either true players or the idle rich, is home to a collection of beautifully classic, time-worn axes. Most of us merely gaze and drool. The repair shop, under the watchful precision of Brian Dunn, is so top-flight that ailing Martins arrive from distant locales for loving repair and restoration. One of the pleasures of walking into Rainbow is to hear some anonymous cat you've never seen before holding forth like the reincarnation of Joe Pass blowing away on "In Walked Bud." Wow.