I've had great success with throwing an overdrive(not distortion) pedal in front of an already dirty amp. Specifically, I use the MXR ZW-44 overdrive. It works great for tightening up a some what loose or muddy distorted sound, and just puts it over the edge into metal meltdown (if you want), or it can act like a little treble boost. One problem with getting a good chunky crunch is too much bass. In my experiance, of all the amps I've played, the bass is either too much or not enough. This is where the overdrive comes in. I like to set my amps dirty channel to give me a good classic rock to slightly hard rock and then switch on the overdrive pedal when I need to tighten things up and add a little more gain. Plus, it can give you a really sweet bluesy crunch through a slightly clean channel. On it's on through a clean channel it is possible to get in the AC/DC range, but not much more. But it really shines through an already dirty amp.

For the chorus, I love my Boss CH-1 Super Chorus. It has a great tone and is fairly versatile. There's a review of it in the "Gear Review" section.

For the wah, you can't go wrong with a Dunlop Cry Baby. I have the "original" model, but they have several other models that are defanately worth checking out that are more versatile.

I can't help you out with the sustainer, but I will say that the overdrive will help with that some.

The main thing is, you need to go to a stor and try some pedals out for yourself. The best thing is to try it out on your own gear if it's possible.

Good luck in your tone quest, and keep us posted on what you try/buy!