I think there's a strong case for both sides of the argument. For suicide, there's the severe stomach problem he had (although I think I heard somewhere that was cured at some point) and of course the issues he had with being in the public eye, along with everything else you've heard before.
But, there's also a lot of evidence for murder. For example, in his supposed suicide note, the only part of it that clearly refers to suicide is at the end of the note, and this part is in drastically different handwriting (experts have analyzed it extensively). Many believe that he was planning on retiring, and in that context, the note (aside from the ending) makes much more sense. A lot of fans think that this is how Courtney may have been involved. Kurt would be worth more to her dead than alive. I don't really believe that completely, but I do think that, if he was murdered, she had a hand in it. Also, there was something like three times the amount of heroin in his body that would incapacitate the heaviest addict within seconds. So, how would he have the strength to pick up the gun and shoot himself? Also, his credit card, which was found in his wallet with his body, was used days after he was shot.
Also, a private investigator was hired by Courtney to try to find Kurt after he escaped from the rehab/detox centre in L.A. The investigator searched every room in the house except the room above the greenhouse (which was where the body was found). The male nanny of the house helped with the search of the house, and didn't say anything about the greenhouse. Because of this, a lot believe he could have been involved with the possible murder. Finally, the police reports were done very carelessly, because they thought that it was a suicide, case closed. There's other things too, like the position of the gun (across Cobain's body) and the fact that there were no fingerprints on the gun.
Personally, I'm not completely sold on it, but I think he was murdered.