I'm thinking of just broad-categories, to get people going (like "movies"+"Genesis", so you can try out a bunch of games you might not have tried otherwise). But above he brought up a good idea.. like Speccy. Retro Gamer is forever going on about Repton and Dizzy (Spindizzy?) and other popular Spectrum games. Perhaps one months theme could be "Dizzy games" or perhaps "Spectrum games" ..
jeff