I used an aboleth and its skum servitors (including a non-standard Giant skum-- which is just fun to say) to very good effect at the start of our current 3.5 campaign. The first "dungeon" was an open-air ruin in the middle of the jungle, and all the structures faced in towards a deep, murky central pool. The pool not only provided the aboleth with cover, but also allowed it to strike any point it wanted in the ruins. Oodles of fun-- even once the party figured out how to activate the ruin's eldritch machine and launch the pool, monster and all, into the cloud layer.