The Artifical Sun is actually an amazing wonder that's a bit underrated if used on its own. It's able to keep any solar panel within 6 hexes of its edge operating even at night and heat the surrounding area, much like the Mohole Mine. What I usually do is put a power cable around it in a ring, then have a three hex long cable go off each corner, put a scrubber at the end of each cable and put a circle around them, then connect them to split the area within the Artifical Sun's radius into six sectors. After that, I put six large solar panels and two small ones in each sector, which I think gives an extra 204-408 power production (depending on if you got the right breakthrough)
The Mohole Mine is a godsend if you're running low on both metals and rare metals, but is useless if you only need one since it stops working when there's no space left for one or the other. The Excavator is nice if you need concrete, but with the Mohole Mine and it (on top of every still-functioning mine) producing waste rocks, you're unlikely to need it that much.
The Omega Telescope provides 5 breakthroughs, which greatly increases your chances of finding one you really like. Beyond that, it also gives a flat 20% boost to research, meaning you can get those techs a bit faster. Once you've got all the breakthroughs you can and researched everything, it's more or less useless.
Project Morpheus is a neat one that gives traits out randomly, including rare traits sometimes, but you have no control over which trait it gives.
The Space Elevator is one that's a bit iffy. Usually, if you're able to build it you've already become almost completely self-sufficient, so you aren't likely to need to buy resources off it unless there's something you're not producing enough of or at all.
The Geoscape Dome is, until they add in dome connections, practically worthless. It uses the same amount of resources (and takes up just as much space) as the Mega Dome, but loses two ninths of the buildable space (six large build spots) to that hill in the center, meaning that it has only a bit more space than the cheaper Oval Dome with 18 large slots to the Oval Dome's 14. I make a point to just ignore the Geoscape Dome because it'd only be worth using as either a park dome or residential area... when we can connect domes, that is.