Recommended: Giftster. Lists can be public, shared or private. Items available online or not online can be listed, and you don't have to register to reserve something from someone else's list. Their URL fetcher makes adding an item by pasting the link very easy - it can obtain the items name, description, price and image from the pasted link.
Also ran: Giftwhale. Laborious adding items, reservation system broken when tested, the confirmation email providing a dud link. Generally error handling is poor. But the site largely worked on my ancient smartphone!
Also ran: WishList.com. All prices shown as dollars. Registration required just to reserve an item.
Also ran: wishlistr. Only one list per account.
Also ran: Whimventory. Doesn't support simple text items - everything must be available online.
Also ran: Wishmindr. Doesn't support simple text items - everything must be available online. Private/ideas lists not supported. Bookmarklet (browser button) somewhat clunky.
No longer recommended: Amazon. Very Amazon-centric since some changes last year: links to other sites pasted in usually get subtly rendered disfunctional, and they have dropped support for their 'Wish from any site' browser button. The replacement 'Amazon Assistant' is a gross invasion of privacy.
Unsuitable: DreamList. US-only site, seems more aimed at money pledging.
Unsuitable: Wishy.gift. Only for Facebook users.
Unsuitable: Wishtack. Facebook or Google authentication required to view a list. Annoying home page.
Unsuitable: WishyBox. Facebook, Google, Twitter etc authentication only. Seems that registration is required to reserve items.