Good thinking, RichCsigs.
Generally and ideally speaking, you should have a "who to contact" list filed with your other important papers- wills, stock certificates, etc. If you want an extra bit of insurance, actually include it in printed form as part of your will, or on a videotape or computer disc to be viewed after your demise (perhaps kept in a safe or your lawyer's office).
If you're a site subscriber and you die, that website is technically a potential creditor of the estate, and would actually need to be notified of your passing...and possibly even reimbursed depending upon timing and your account setup. That doesn't mean, however, that they'd notify your online buddies.
If you have their email or RW addresses, then its not a big deal. If its on a password protected account, things get tougher- again RichCsigs basically did it right.
So, you need someone you trust to take care of that- either someone in their official capacity as your executor or someone with power of attorney, or someone in their unofficial capacity of Good Buddy.
Of course, here I am a lawyer, and I've done NONE of that- Do as I say, not as I do!
OTOH, perhaps some enterprising soul can set up a website, perhaps?
(Ebituaries.org already exists...sort of.)