I have a Diamond Wool brand pad (one of the ones you can shim if you need to) and I adore it. I haven't been able to ride in it a ton because my mare is crazy wide and doesn't need a 2inch pad, but the times I have ridden in it have been great.
The only complaint I have with it is that it's an ugly brown color. Thankfully I'm a handy enough hand sewer that I was able to sew prettier cloth on to it, but yknow.
One day, when/if I get a narrower horse, I will be using this pad 24/7 because it's just that great.
I also have an Abetta Polar Fleece pad ( Saddles Tack Horse Supplies - ChickSaddlery.com Abetta Polar Fleece Reversible Pad
) that I got on Ebay for about $25, three or so years ago. Obviously, for that price, it's not the classiest pad ever but I have been using it on a near daily basis for 3 years and it's still going strong. I did cover it with pretty cloth about a week ago because the fleece was starting to pill and look gross, but otherwise it's doing well.
It's a thinner pad (about 1inch thick) but my mare is wide enough that anything thicker bothers her (since it makes the saddle fit "not right") and anything thinner is too thin (she's 27 and just a bit sensitive about these things, haha).
If you want to go all the way and really get something nice, you can't go wrong with 5 Star pads ( - 5star Equine Products
). I have never heard one bad thing about them and wool is always a great choice for a saddle pad.
They are pretty expensive but I've heard that they last for practically forever.