Courtney Love had him killed because he was about to leave her ass broke on the streets :p
Since he "suicided" she inherited all his money and Nirvana rights/royalties.
She also supposedly had a member of her band (hole) killed in a similar manner.
actually that is not all that unlikely...
listen to the song "you know you're right" it contains the line "I will move away from here, you won't be afraid of fear, no thought was put into this I'd always known it would come to this"
being cobain the last sentence sounds somewhat desperate, but maybe he's just talking about divorse instead of suicide...
And some people seem to think that the letter he left was not a suicide note but a letter about him wanting to give up musik. I don't know much about that.
What about you Pho? I think i saw someone write that you know all conspiracy theories on the web and which ones are true...