You might also look into setting up your own site as a delegate for another OpenID provider. That way, you can use your own custom URL, but not worry about security and maintenance as mentioned already. However, it's not very difficult, so it may not meet your criteria :)
As an example, you would add this snippet of HTML to the page at your desired OpenID URL if you are using ClaimID as the OpenID provider:
<link rel="openid.server" href="http://openid.claimid.com/server" />
<link rel="openid.delegate" href="http://openid.claimid.com/USERNAME" />
So when OpenID clients access your URL, they "redirect" themselves to the actual provider.