I've found uses for all the available heavy weapons, apart from heavy bolters.
I don't use lascannons a lot but they are still very good guns. They are expensive of course, but without a few of them in your list you will have big problems with things like obliterators. The extra point of strength makes a big difference to your chances of killing most vehicles as well, with the effect that it does generally make sense to pay 20% more for that combat squad - if it is going to be shooting at tanks.
Most people go for missile launchers or multi-meltas. Either is good but I would suggest a mixture rather than going all one way or the other. About half and half is probably best.
Plasma cannons can be amazing, though they usually aren't. Having a squad with a plasma cannon ready to fire if a transport pops can be devastating though. Negating fnp can be huge.
Personally I do go for fists, which I consider to be offensive, rather than defensive weapons. It wouldn't be crazy to not take them, but I would miss them I'm sure. Drizzt's point that they mostly help in situations you are winning anyway might be true though. If you are using a lot of tactical marines then you can be less precious with them and throw them at things like obliterators, which can win games, but only if you have a fist. Otherwise you need somebody else.
For special weapons I think meltas are the only choice. They are so good against so many of the key units you need to kill. Plasma guns don't justify their cost for one more shot, at far less power. Flamers are a luxury, and are only really good at things you could shoot with your bolters or charge anyway. I'd want to have a flamer somewhere in my list, but I tend to field a redeemer which ticks that box nicely.