If you use bounce cards a lot and beat up your gear, then the Honl Speed Gobo / Bounce Card is worth considering. The $14.95 price does give you a lightweight, durable and versatile tool that will survive rough treatment and pull double duty for you if you ever need a gobo. For those who don't use much bounce flash or don't mind carrying a handful of 3x5 index cards with them on shoots, there are cheaper alternatives. Keep in mind, you also need to be able to attach the card to your flash. You can either do this with Velcro or with Honl's speed strap, a $9.95 accessory that can be used with a variety of Honl products.
Full disclosure: Honl provided the author with a Honl Speed Gobo / Bounce Card for inclusion in the David Busch Quick Snap Guide to Photo Gear.