I have a list of 8 objective structures that I want to draw up:
1) Wraithgate
2) Exodite Silo
3) Sensor Tower
4) Exodite Homestead/Eldar Bunker
5) Power generation sail masts
6) World Stone cairns
7) Gate of Vaul

Communications tower
The first 3 are done, and the 4th I'm detailing now. I've done some work on the 5th, but I haven't really settled on how I want the base of the mast to look. The 6th is really just a stone henge rip-off, which may be easier to make with plasicard strips.
The 7th isn't started yet, but I think I've figured out how to make the curvalinear shapes needed to approximate the structure shown on the cover of Swordwind.
As for the 8th, it may get dropped. It really is just an excuse to have another objective use the same tower base and platform as the silo and the sensor tower. To be honest, I haven't really come up with a concept of what a large Eldar transmitter would look like. I want it to look vaguely like a satellite dish, but not so much that it doesn't look appropriately eldar.
In the end, my plan is to use several of the structures on each of my objectives (which will be on 60mm titan bases). I figure a bunker and sensor tower, 2 silos and a sensor tower, two power sails and a bunker, etc. add some scenic rocks and flock, and they should look okay. I plan on going for an exodite or craftworld settler feel.