http://www.darwinawards.com is your friend. :-)
First, get yourself a jar. Then put two tablespoons of salt in it, and one tablespoon of baking soda. Then fill your jar 2/3 of the way full with ammonia. Next completely fill your jar with laundry bleach. Now drop a bunch of pennies into your jar, and HUFF THAT SHIT!
Had a second idea for you sir. Mustard gas is fun, you most likely will die.
You want creative and relatively painless? The latter stipulation will strain the efforts of the former. So many things have already been done.
Anyway, my suggestion is to take an incredible amount of DMT or similarly hallucinogenic substance -- DMT would be ideal, since you would be able to test if there's any validity to DMT being released prior to death. This scenario gives you the possibility of getting a jump start into the next realm, if there is one. The actual method of killing yourself? Asphyxiation might be ideal, like carbon monoxide or something, since you'll basically die in a choking sleep. A lot of inceptive potential here, considering DMT has some thought to be involved in stages of sleep, though I don't know if that's been verified or was invalidated recently.
Take 20x the recommended dose of OxyContin. While you're waiting for them to kick in, pour gasoline throughout your house. light a match in the room furthest from where you want to die. Don't bother waiting for the show.
You're family with be pretty upset about your death. No house to live in is just the cherry on top.