OpenId

Check out this handy reference to enable openId on your website. OpenId enables your clients to login to your website using one single userid/password, taking the hassle out of remembering multiple userids/passwords for each site. If you are using yahoo, gmail, blogger, wordpress etc. you already have openid, you just need to enable them and use it.

Check this handy reference:
http://www.plaxo.com/api/openid_recipe

To learn more about openId, check out the official website at:
http://www.openid.net