By the way, most corals will fight with any other coral they touch. Unless they're the same species, you'll probably see some damage where they're touching. Damage can be anything from a little "burning" to whole polyps dying.
If you get leathers, make sure they're downflow of any LPS, and don't place them within a few inches of LPS. Their toxins can irritate LPS.
On the other hand, most LPS will sting to death anything they can touch. Watch out for sweeper tentacles at night on your LPS to make sure they can't reach neighboring corals. The only exceptions I know of this are corals of the same species can touch, and hammer and frogspawn can touch (and torch with hammer, to some extent). I don't know about SPS at all.