Maybe not exactly what you're looking for, but Mike's Amazing World of Comics has a feature where you can look at covers put out during a given month & year (it will also how them by cover date so be careful you've got the right setting).
http://www.dcindexes.com/timemachine/You can select it to look at all publishers or some specific companies (so far DC, Marvel, Archie, Charlton, Dell, Gold Key, Harvey, Dark Horse & Image).