These are nice because they have stiction-free travel, unlike telescoping suspension posts, there is no initial stiction to overcome. The suspension mechanism works in the direct path of the natural travel of the rear wheel.
The parallel linkage design also tends to have less side to side movement for the seat post.
BodyFloat Isolation Seatpost: The BodyFloat isolates the vibrations between the vehicle (your bike) and the motor (you) so that you can be more efficient with your pedaling and enjoy a more comfortable ride. It provides up to 1.5″ of almost perfectly vertical travel.
Cane Creek 3G Thudbuster Long Travel Suspension Seatpost
Cane Creek 3G Thudbuster Long Travel (this is the one I have used for years): The Thudbuster LT is one of the more expensive suspension seatposts but it is higher quality and provides 3″ of travel!
Cane Creek Thudbuster Short Travel: The Thudbuster ST is very similar to the LT but it only provides 1.3″ of travel and it is a little less expensive when compared to the LT.
Telescoping style suspension posts offer an economical option but they tend to have a little more side to side movement of the seat that can be a little weird!
But these can be a great option to keep the price down and smooth out the road a bit.
Tamer Weekender: This post provides about 2″ of travel and uses a spring and elastomer system.
Avenir: This seatpost provides 1.75″ of travel using a spring and elastomer. It also comes with shims to fit various sizes of bikes.
IMPORTANT! Suspension Seatpost Sizing
You will need to determine the diameter and length of your current seatpost and order the same diameter and same length (or longer) suspension seatpost.
Most seatposts have the diameter noted on the seatpost but you may need to remove it from the bike to see it. The length may also be noted but that may be something you will need to measure on your own. (1 inch = 25.4 millimeters)
In some cases you may not be able to order the same diameter size suspension seatpost, so you will need to order a shim that will fit your seat-tube (exterior part of the shim) and the suspension post size (interior part of the shim).