I agree with MyBoyPuck and Luvs2Ride - Gel pads aren't that effective because - well, MBP pretty much explained it. I used one, and it did pretty much nadda for my TB's sensative back.
I like Thinline, just as mentioned. I am currently saving up for the Thinline Comfort Sheepskin 1/2 Pad - I really like the look of that one.