Pat from the Silver Age Comics blog has started up a new series looking at the various aliens that went up against the Dynamic Duo. Sci-fi stories appeared here and there throughout the Golden and Silver Ages, but it is the Jack Schiff era of the late fifties and early sixties that most people associate aliens with Batman. Pat is going to be working backwards, starting in the first post with the significant stories from 1963-1964. You can check it out here. Pat also did an interesting post on the origins of the Silver Age Cat-Man a couple weeks back, who appeared in three Batman stories in the Silver Age.