I'm another who loves the Crystal Visions backs, and also the Waking the Wild Spirit Tarot backs - borderless, lively and colourful, yet not too glaringly bright. Wish the cards themselves were borderless, too.
Other backs I like are the Shadowscapes, Mystic Dreamer and Robin Wood. I like backs that closely reflect the mood or style of the card designs.
I don't particularly care for cross-hatched RWS backs, but the PCS Commemorative deck is an outstanding exception. Of all the decks I own, the backs of the Spiral Tarot are very disappointing: an unimaginative fine-line double spiral on a flat cobalt blue background. Ugh.