The biggest problem with suicidal people is their irresponsibility. What if they hit someone when they jump off the bridge, balcony, plane or window? They hit someone, then they can sue that person for ruining their suicide (assuming both people are alive) and the 'victim' can sue for injuries.
So jumping off something is a bad idea in general, so what's the right way? Well, most of the ways I can think of are irresponsible in some way. Let's say you gas yourself at home. Well this can really be dangerous as you can blow up whole bunch of people around... So gas is a wrong answer either.
Suffocating in your car is a bit better, but again - who wants a smelly car after you die? After a few minutes with the engine fumes, the whole car will start to smell like car rallies were held inside the car. And you - well not you, but your husband, e.g. - won't be able to get rid of the smell without changing most of the interior.
Another way is shooting yourself. Don't do that unless you hold a brick or something on the other side of your head and you're standing on a huge plastic bag which can just be zipped up. Have you ever bled on your favorite shirt? So you know how hard it's to get blood from something, right? Do this only if you really hate the owner of the place you're planning to kill yourself on.
Then there's slitting your wrists. However this is not really nice either as someone will have to replace the bath tub (assuming you have chosen bath tub) as the blood gets off it really hard (after some time). Plus it's not pleasing to deal with a soaked corpse...
Well, we're almost done with this little list. What about pills? You don't really leave that much mess with that, right? Well yes and no. If you're sure that the dosage you're about to swallow is the right one, then I'd say it's probably the easiest way to off yourself. However, when you don't take enough pills, you'll probably end up somehow damaged (inside, outside, whatever) and someone will have to take care of you and it's really awkward to deal with suicide-attempters.
Of course I haven't gone through all the possibilities. You can use electricity (danger of fire), jump in front of a train (too much mess and you could piss off all those people rushing somewhere), ... But generally there is no safe and responsible way to off yourself. I guess government should make a 'Suicide Point' where people can kill themselves easily. However, the governments are greedy and want more and more tax payers. So dream on, sicko!