I agree with the negative comments towards gel pads. In addition, they do not breathe at all and your horse's back will get HOT under it and stay HOT.
I have heard many positive things about ThinLine products. And I personally love to use sheepskin pads. Sheepskin is naturally breathable and shock absorbing. I even feel like my saddle is more comfortable (more "springy") when I have a sheepskin pad under it. I may have to look into this ThinLine/Sheepskin pad posted by MIEventer! Sweet!!
Monte - 15 year old Paint/TB
Auric - 13 year old Arab