A sequel to this post. Most of this comes from Orion's Arm, as usual. But not all.
Ederworlds/Gravity Balloons. Just learned about them tonight. A big bubble of air enclosed by a solid exterior, hundreds of thousands of kilometers across. No artificial gravity. Fun stuff.
Banks Orbitals. Essentially a ringworld in miniature, a few million kilometers wide.
Credit: Matthew C. Johnson
Ringworlds. Well known by now, no need to describe them.
Credit: Harry Frank
And the ultimate space construct, the Dyson Sphere: