Some sustained forces can be achieved using gravity on a tilted platform. When a sustained force is desired, a centrifuge or very large linear device is required. Single DOF linear motion systems have been used as a 'seat shaker' to give some vibration sense, although acoustic systems are more often used for this purpose. The robotics and nanotechnology folks have published a fair bit on these devices, although most of the information is on positioning control and not motion simulation. The most common types of actuators are pneumatic, electrical, and hydraulic.
Hydraulic systems are more powerful and accurate but also more costly.
Pneumatic and Hydraulic systems require compressors that may be noisy. Electric systems are quiet but not nearly as responsive. Motionware update 'Motionware' from Virtual Motion is a markedly different approach to motion simulation. Instead of relying on mechanical motion, it applies a tiny current to electrodes located behind the ears to stimulate the vestibular nerves. The resulting nerve activity mimics the natural response to change in orientation of the head.