The best known half pad is the Ogilvy Memory Foam Jump Half Pad. It provides increased stability and fills out the gaps to enable a better fit for the saddle. The Ogilvy Half Pad Covers are washable. The memory foam can be easily removed from the half pad.
Ogilvy also makes a dressage version of the Ogilvy Memory Foam Dressage Half Pad as well.
Note that both the Dressage and Jump Half Pad can be customized as per your choices. Custom orders take anywhere from 6 to 10 weeks.