Rugs, Carpets and Carpeting - Carpet Questions

My wife and I just bought our first home and we are going to have new carpet installed before we move in. My wife wants to use berber carpet and I think it's a good idea. My question is, what kind of pad should we buy? I've heard several times that it's the pad that makes the carpet good. But what I don't understand is, what makes a good pad? If anyone can help me with that I would really appreciate it.
We're looing at buying the carpet from Home Depot. They seem to have a good selection and also pretty good prices. Any tips or suggestions are really appreciated!

There is more to pad than making carpet good.The yarn ,the density,the backing and the material used are all factors.To answer your question about the pad...Do not go over 3/8 padding.rebond pad is good for the money.The denser the pad the better not the cushier.At least 8 pound density is reccomended.Locignotile@hotmail.com

Carpet manufactures all have their specs. None of them will warranty a loop pile berber over anything thicker then 3/8" and it must have a density rating of 8 lb or greater if using rebond padding. I like to use a 50 oz synthetic felt under all my loop pile installations, but most of the time the extra expense makes the homeowners come back down to rebond padding. The more flex in the backing, the more the carpet will delaminate. Make sure the seams in the carpet are seam sealed with latex or acrylic seam sealer!!!!! It takes special talent to seam loop piles so the seams are invisible. Basically the loops make a pattern that interlock. If you get 2 loops side by side or a gap in the interlock, the seams will look bad and show. Berbers are going out of style around my neck of the woods. As the wear factor isn't what it use to be either. If you do decide on berber, make sure not to use a vacuum with a beater bar. They will cause snags and runs in your carpet.