What about public key authentication akin to passwordless SSH logins? You can generate several keys to be as anonymous as you wish and there are several options where to store your public key. One option is to store it on a public keyserver; another is to upload it to the site you wish to access. The advantage is that the only data travelling across the net is the public key. OpenID still relies on passwords. If you want to be able to have multiple identities online, you'll have to create multiple OpenID accounts. The unqestionable advantage of OpenID is that it does not require special browser support.