Gotcha!'s Map Pack 3:
viewtopic.php?f=24&t=12224Requires a special installation, and has a lot of maps as well as a ton of objects.
Also UniTec has a few prebuilt bases, as well as dispensers, teleporter target and turrets:
viewtopic.php?f=61&t=11062Grif's constructor mod(build things while the game is running):
viewtopic.php?f=61&t=17285Pete's Dirt Modules -
viewtopic.php?f=61&t=17853Dutchsmoker's Unified Bunker Defense and Construction Industries:
viewtopic.php?f=61&t=19656My "Traps Incorporated" collection of traps:
viewtopic.php?f=61&t=20892 Roast Veg's Photon Collider:
viewtopic.php?f=61&t=20828Findude's Counters(death counters, irl new years counters, game counters):
viewtopic.php?f=61&t=20741Yoman's End-User Research:
viewtopic.php?f=61&t=18385MaximDude Corp(has some neat doors and turrets, as well as a silo):
viewtopic.php?f=61&t=17243Numgun's BW and AAL have some modules(bw has B24 issues, beware):
viewtopic.php?f=61&t=18479This is all just off the top of my head and the first page of search.