RollerCoaster Tycoon

This set includes many terrain conforming path covers as well as edges, railings and terrain covers perfect for any custom path work in your next park.
Set goes in Style\Themed\ just as normal scenery.

Weber's Foliage Set, updated version 1.1. Includes boulders, grass, small flowers, ground cover, felled trees, houseplants, and 3 new trees.

NightHawk's Invisible Path. (alternative to Belgabor's Invisible Doodads)
Place the "Arknot" folder in your RCT3 "Paths" folder.
Note: As can be seen in the screenshot, these invisible paths do not let some scenery or Peeps be seen underneath them. With proper placement this can be used to hide objects you don't want to be seen.

ImagineerJohn's Coaster Kit. Contains 16 Ride Events, including Waterfalls, animated brake sections, timed lowering loading platforms, SplashDown Sprays, and more.
 

Walt Disney World Railroad Walter E Disney by Ghostscout.
This CTR-Ride requires RCT3 WITH BOTH ADDONS Soaked/Wild! The installation without Addons will cause RCT3 to crash.

Fort Wilderness Railroad by Ghostscout.
This CTR-Ride requires RCT3 WITH BOTH ADDONS Soaked/Wild! The installation without Addons will cause RCT3 to crash.

Galaxy Flyer CFR by Samplerocker. Can be found under Gentle Rides in the RCT build menu.
Installs to Style\Custom\ folder. (if you don't have a Custom folder under Style, you must create one)
This CFR only works in RCT3 WITH BOTH ADDONS Soaked/Wild! Installation without Add Ons will cause RCT3 to crash.
This ride uses about 2,500 faces and 6 textures in the sizes 4x4 and 64x64 pixels.

Loubauder's Disney Jungle Cruise CTR. Requires Revolutionary Rides Invisible Track.
The boats are not powered and thus require you to use block break sections to push the boat along.

Disney Tram by Ghostscout.
This CTR-Ride requires RCT3 WITH BOTH ADDONS Soaked/Wild! The installation without Addons will cause RCT3 to crash.
(Note: the shown station is not included)

MK I, IV, V, IV, and VII Disney Monorails by Ghostscout. Versions in multiple colors and textures. MK V & VII trains hold only 2 people per car, all the rest hold 4 per car.
You will need to download the "Monorail Set/universal monorail" and install it to use this CTR. This CTR-Ride requires RCT3 WITH BOTH ADDONS Soaked/Wild! The installation without Addons will cause RCT3 to crash.
(Note: the station shown is not included)
 

Disney's California Adventure - World of Color Items by AzoRctMan. Includes Laser, water jet, and mortar.

This set includes lamp posts, stanchions, straight and diagonal hedges, a ride operator console, some new path edges, railings, terrain covers, shuttle loop parts, tables, chairs, trash bins, windows, doors, counters, billboards, and more.

This set contains circus tents, decorative canvas roofs, stadium benches, skeeball machines, pay phones, fancy trims, angled railings, angled walls, and more.

This set contains circus tents, game backdrops, umbrellas, windows, 3h roofs, railings, circus signs, circus paintings, and lots more.

This set contains rustic walls, 1h roofs, wooden floors, marble columns, wooden railings, shutters, bedrock walls, signs, windows, and a lot more.

10 Inversion Intamin CT by Ciniapaes. Originally posted on RealTycoon3.com

Boomerang CT by Cinipaes. Originally posted on RealTycoon3.com

Arrow Corkscrew CT by Cinipaes. Originally posted on RealTycoon3.com

Apocalypse CT by Cinipaes. Originally posted on RealTycoon3.com

Banshee CT by Cinipaes. Originally posted on RealTycoon3.com

Batman: The Ride CT by Cinipaes. Originally posted on RealTycoon 3

This set contains generic billboards in three styles... Single-sided, double-sided, and wooden backed.

This set features updated roofs with better textures and thicker beams and posts.
 

This set contains mostly interior pieces, decor, and furnishings.
 

Updated Alpine Village objects includes stucco walls, windows, doors, path covers, chimneys, roofs, shutters, and curtains.