2: Sub rumble.

For nice deep ambient sub rumble in tracks, one of the techniques I sometimes use is to get a nice subby kick or bass sound, and run it through some monstrous cathedral size reverb.
I then sample the result, pull out the initial sound so I end up with just the deep verb on it`s own.
Then you can slap this under your kicks in a track, sidechained to the kicks, and it really gives a nice cavernous rumble.
For some interesting sub madness sometimes it`s also nice to make a subtle bass melody using this sample, and have that rumbling away under the kicks.