This is something I've thought about a lot.
My mom had a disease that involved a great deal of treatment and it wasn't a very common disease so she had found a wonderful support group online. I helped her start a blog (http://www.jarrett.ws/dale) and after she lost the battle with the disease I was the one who updated her blog to share the bad news. That is still the latest post on the blog, having left it untouched since then. I make sure to renew the domain and take care of it for her.
The fact is that death and the Internet is still quite nebulous. Companies don't really address it, the law hasn't covered it, etc.
We knew mom's passwords so I didn't have wrangle control or anything, I went into her email accounts and collected any emails or mementos I wanted to keep. I unsubscribed her from mailing lists and discussion groups, generally got her digital life in order.
The idea of handling online property is something I'd even considered bringing to YC as a business concept, but I couldn't find a solid base for it. Even aside from emails, blogs, and such, I had considered the idea of virtual wealth in MMOs and such.
I actually expect Facebook to be the first social network to really begin addressing this issue, as they seem more intent on generating a map of relationships rather than building new ones.
As to answer your question, then it needs to be in your will, as a first step. You can avoid the legal wrangling by putting the info in your will as to your wishes and login/pass.
Once companies begin to accept that they're holding information and property of individuals, then they'll reach an understanding and process for handling deaths and the transfer of this information.
I hope.