The stock here represents what's happening in just about every field of publishing today: students can grab a last-minute Gertrude Stein for their literature class, then rummage through the homages to cult pop-culture figures. Late hours at the downtown location ('til midnight on Friday and Saturday, 11 PM the rest of the week) are a plus. Subway: 6 to 68th St./Hunter College. Other locations: 137 E. 23rd St., at Lexington Ave., Gramercy, PHONE: 212/505-2021; Subway: 6 to 23rd St. 716 Broadway, at Washington Pl., Greenwich Village, PHONE: 212/529-1330; Subway: R, W to 8th St. 1 Whitehall St., at Beaver St., Lower Manhattan, PHONE: 212/742-7025; Subway: 4, 5 to Bowling Green.