After reading this post from O'Reilly Radar on several big-name companies joining the OpenID Foundation, I decided to give OpenID a try myself. One of the providers recommended by the foundation was VeriSign, which sounded reputable to me, so I went ahead and got one from their Personal Identity Provider (PIP) site. Easy enough -- you choose a user name, a password, put your email in, then you get a so-called "OpenID access URL" of the form username.pip.verisignlabs.com.
To test my brand new OpenID, I went to one of the sites referenced on the PIP page, stikis.com. I chose the OpenID authentication method, entered the id I got from VeriSign, then I was redirected to the VeriSign PIP page, which asked me to specify for how long I want my trust relationship with stikis.com to last. I chose 1 year, clicked 'Allow', then was redirected back to the stikis.com site, already logged in to my personal start page. When I clicked on 'My Account' inside stikis.com, I saw my VeriSign access URL page at http://username.pip.verisignlabs.com. Pretty clean process. I hope more and more Web sites will accept OpenIDs. Since Google, Yahoo and Microsoft all joined the OpenID foundation, I'm pretty sure you'll be able to use an account you have with any of them as your OpenID (and indeed all of the above companies have announced that they'll be offering OpenIDs).