I've been complaining about Canon's antiquated side-pinch-only lens cap design for years. Finally, Canon has listened and announced new side-and-center-pinch caps. Hopefully they will sell these in bulk packs.
From Canon UK:
New lens caps – designed for greater ease and convenience
Canon's 'Mark II' centre-pinch lens caps. From left to right: 82mm, 77mm, 72mm, 67mm, and 58mm.
Both new lenses also come with newly-designed Mark II lens caps, which incorporate a hook mechanism in the centre of the cover, as opposed to the sides. Simply pinching the hook allows users to quickly remove and replace caps mid-shoot, especially when using lens hoods. The re-designed lens caps will start to be rolled out across Canon’s entire EF lens range from the beginning of January 2013, and will also be available to buy separately.