Can't get enough of this repository of Penguin Science Fiction covers. There's an amazing variety of style but you can clearly see patterns and themes across the different eras. I think my sweet spot may be Into the Computer Age or Strange Fruit (early 70's) but it really is difficult to pick a single favorite anything from this bunch of greatness.

My only complaint about this page is that the images are never available in Gigantic Size but, as luck would have it, there's a postcard set of many of these images, which would certainly suffice in proper dedicated enjoyment.