We know that dweb and dark swarm can be done and I encourage you to use it to do something nice and unique to the map... What else could be done? Psyonic storms? idk, maybe you do.
It's unlikely that there are other unit-sprites that actually have a gameplay effect. DWeb and swarm are the only spells that are actually units (note that broodling creates units, but the spell is a sprite). Well, there also is Scanner Sweep. But I don't think it does anything even if it is placed as a unit sprite.
One might try it out, though.
Nuke targets could encourage nuking, but I doubt it :p
dweb and dark swarm are the only sprites that work, unluckily psis, maelstrom, [insert any other spell here] wont work, bw crashes if you place them =(
oh, too bad. I'd have liked a "death zone" map where you have to pass the "sea of the psionic storm" to get to the most important expansion if the map;)