Here's a nice site showing some tasty examples of the now, nearly forgotten art of designing eye catching single sleeves. It's broken down into catagories for ease of searching with an A to Z of labels as well as general genres like stars, patterns and two colour prints. Above: are two (slightly changed) examples of pleasing on the eye patterns that were designed. These show that simplicity often produces the best results.
This site has some more fine 45 design action..