Underwater epoxy is great. So is cyanocryalite (sp?)(super glue, look for the real name on the back and it will work well) for that matter.
Don't think of Underwater epoxy as glue, so much as a good locking device. It is like playdogh that hardens into a rock like consistancy. It basically can be used to create shim like pices to hold rocks in odd positions. It is also great for holding SPS frags to rocks. It can also be used to plug holes that aptasia live in (a very effective way to kill a few before a problem develops)
For soft corals, use the super glue. Unless they are attached to a rock already, then use the epoxy. Super glue is the best for coral tissue, because that was what it was designed for: to be used in combat situations to close wounds without the need for sutres.
There are a number of types of epoxy that you can get. most are from the LFS. There is the Little fishies brand that comes in 8" of grey or 4" of pink (same price). The pink will fade to white (most likely before the coraline covers it completly) The grey fades but a little less. The pink seems stickier, but it is not sticky enough to really do much in the way of glueing just "shimming". There is also one by Aquarium systems which is green with a white center core. It is the least sticky of them all, but still works. All of these will set you back about 10-15 bucks Locally or less if mail ordered.
I have used a brand from Home Depot that is 1.99 that looks exactly like the aquarium systems product. It is labled underwater epoxy and uses the same or simmalar ingrideints and is listed as non toxic (the others are obviously non toxic). I have used this in my 10 gallon with no problems. If people are interested I will figure out the exact brand.
HTH
Luke