6) Dead Gods: The bodies of dead gods tend to be some of the most promenent solid spaces in the astral plane. They are almost always enveloped in various curtains that conceal there presence at a distance. For the most part, these are like islands of real matter only much much worse. If you don't have business being near them, back off as quickly as possible.
Good stuff Celebrim,
I like the idea of the floating fragments of dreams - I think that could give a lot of flavor to the combat.
FYI, not sure if I have mentioned it but this is 4e campaign.
The last part that I have quoted from you, is exactly the reason the PCs are sailing the Astral Sea. They are seeking Haemnathuun, a dead Primordial and need his heart (or a piece of it) to open an ancient artifact from the Dawn War. While most of my encounters will be at specific locales in the Astral Plane, I wanted one within the sea itself, hence the Dreadnaught.
So far my favorites are the Psychic Storm and the dream fragments to spice up the fight.